diff --git a/ChangeLog.md b/ChangeLog.md
index dc8be88d34a52..ae32353d202ad 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -48,6 +48,13 @@ See docs/process.md for more on how version tagging works.
 - emcc will now error if `MINIMAL_RUNTIME_STREAMING_WASM_COMPILATION` or
   `MINIMAL_RUNTIME_STREAMING_WASM_INSTANTIATION` are used with `SINGLE_FILE`.
   These are fundamentally incompatible but were previously ignored. (#24849)
+- Added two new proxying directives. foo__proxy: 'abort' will abort program
+  execution if JS function foo is called from a pthread or a Wasm Worker.
+  foo__proxy: 'abort_debug' will do the same, but only in ASSERTIONS builds, and
+  in non-ASSERTIONS builds will be no-op.
+  Use these proxying directives to annotate JS functions that should not be
+  getting called from Workers. (#22648)
+
 - `--export-es6` flag was added to `file_packager.py` available when run 
   standalone, to enable ES6 imports of generated JavaScript code (#24737)
 
diff --git a/src/jsifier.mjs b/src/jsifier.mjs
index b7d9dd17e2a94..612bc638df91e 100644
--- a/src/jsifier.mjs
+++ b/src/jsifier.mjs
@@ -17,6 +17,7 @@ import {
   ATPRERUNS,
   ATMAINS,
   ATPOSTRUNS,
+  ENVIRONMENT_IS_WORKER_THREAD,
   defineI64Param,
   indentify,
   makeReturn64,
@@ -437,39 +438,38 @@ function(${args}) {
 
     const proxyingMode = LibraryManager.library[symbol + '__proxy'];
     if (proxyingMode) {
-      if (proxyingMode !== 'sync' && proxyingMode !== 'async' && proxyingMode !== 'none') {
-        throw new Error(`Invalid proxyingMode ${symbol}__proxy: '${proxyingMode}' specified!`);
+      const possibleProxyingModes = ['sync', 'async', 'none', 'abort', 'abort_debug'];
+      if (!possibleProxyingModes.includes(proxyingMode)) {
+        throw new Error(`Invalid proxyingMode ${symbol}__proxy: '${proxyingMode}' specified! Possible modes: ${possibleProxyingModes.join(',')}`);
       }
       if (SHARED_MEMORY && proxyingMode != 'none') {
-        const sync = proxyingMode === 'sync';
-        if (PTHREADS) {
-          snippet = modifyJSFunction(snippet, (args, body, async_, oneliner) => {
-            if (oneliner) {
-              body = `return ${body}`;
+        snippet = modifyJSFunction(snippet, (args, body, async_, oneliner) => {
+          if (oneliner) {
+            body = `return ${body}`;
+          }
+          const rtnType = sig && sig.length ? sig[0] : null;
+          const proxyFunc =
+            MEMORY64 && rtnType == 'p' ? 'proxyToMainThreadPtr' : 'proxyToMainThread';
+          var prefix = '';
+
+          if (proxyingMode == 'sync' || proxyingMode == 'async') {
+            if (PTHREADS) {
+              deps.push('$' + proxyFunc);
+              prefix = `if (ENVIRONMENT_IS_PTHREAD) return ${proxyFunc}(${proxiedFunctionTable.length}, 0, ${+(proxyingMode === 'sync')}${args ? ', ' : ''}${args});`;
             }
-            const rtnType = sig && sig.length ? sig[0] : null;
-            const proxyFunc =
-              MEMORY64 && rtnType == 'p' ? 'proxyToMainThreadPtr' : 'proxyToMainThread';
-            deps.push('$' + proxyFunc);
-            return `
-${async_}function(${args}) {
-if (ENVIRONMENT_IS_PTHREAD)
-  return ${proxyFunc}(${proxiedFunctionTable.length}, 0, ${+sync}${args ? ', ' : ''}${args});
+            if (WASM_WORKERS && ASSERTIONS) {
+              prefix += `\nassert(!ENVIRONMENT_IS_WASM_WORKER, "Attempted to call proxied function '${mangled}' in a Wasm Worker, but in Wasm Worker enabled builds, proxied function architecture is not available!");`;
+            }
+          } else if (proxyingMode == 'abort' || (proxyingMode == 'abort_debug' && ASSERTIONS)) {
+            const insideWorker = ENVIRONMENT_IS_WORKER_THREAD();
+            prefix = `if (${insideWorker}) abort("Attempted to call function '${mangled}' inside a pthread/Wasm Worker, but by using the proxying directive '${proxyingMode}', this function has been declared to only be callable from the main browser thread");`;
+          }
+
+          return `${async_}function(${args}) {
+${prefix}
 ${body}
 }\n`;
-          });
-        } else if (WASM_WORKERS && ASSERTIONS) {
-          // In ASSERTIONS builds add runtime checks that proxied functions are not attempted to be called in Wasm Workers
-          // (since there is no automatic proxying architecture available)
-          snippet = modifyJSFunction(
-            snippet,
-            (args, body) => `
-function(${args}) {
-  assert(!ENVIRONMENT_IS_WASM_WORKER, "Attempted to call proxied function '${mangled}' in a Wasm Worker, but in Wasm Worker enabled builds, proxied function architecture is not available!");
-  ${body}
-}\n`,
-          );
-        }
+        });
         proxiedFunctionTable.push(mangled);
       }
     }
diff --git a/src/lib/libwasi.js b/src/lib/libwasi.js
index 2d3b143f0969a..8b0b182fb9181 100644
--- a/src/lib/libwasi.js
+++ b/src/lib/libwasi.js
@@ -262,6 +262,10 @@ var WasiLibrary = {
     if (printCharBuffers[1].length) printChar(1, {{{ charCode("\n") }}});
     if (printCharBuffers[2].length) printChar(2, {{{ charCode("\n") }}});
   },
+  // When we don't have a filesystem enabled, we do not need to proxy fd_write
+  // to the main thread, because all we do is log out() and err() calls.
+  // This enables printf() to work from Wasm Workers.
+  fd_write__proxy: 'none',
   fd_write__deps: ['$flush_NO_FILESYSTEM', '$printChar'],
   fd_write__postset: () => addAtExit('flush_NO_FILESYSTEM()'),
 #else
diff --git a/src/parseTools.mjs b/src/parseTools.mjs
index 4aaa67d2e7dbf..460703e0c8b9d 100644
--- a/src/parseTools.mjs
+++ b/src/parseTools.mjs
@@ -1091,7 +1091,7 @@ function ENVIRONMENT_IS_MAIN_THREAD() {
   return `(!${ENVIRONMENT_IS_WORKER_THREAD()})`;
 }
 
-function ENVIRONMENT_IS_WORKER_THREAD() {
+export function ENVIRONMENT_IS_WORKER_THREAD() {
   assert(PTHREADS || WASM_WORKERS);
   var envs = [];
   if (PTHREADS) envs.push('ENVIRONMENT_IS_PTHREAD');
diff --git a/test/pthread/proxy_abort.c b/test/pthread/proxy_abort.c
new file mode 100644
index 0000000000000..7f86949535315
--- /dev/null
+++ b/test/pthread/proxy_abort.c
@@ -0,0 +1,43 @@
+#include <emscripten.h>
+#include <pthread.h>
+#include <assert.h>
+
+// Tests behavior of __proxy: 'abort' and __proxy: 'abort_debug' in pthreads.
+
+void proxied_js_function(void);
+
+int might_throw(void(*func)()) {
+  int threw = EM_ASM_INT({
+    // Patch over abort() so that we can gracefully finish the test without
+    // an unhandled exception hanging the test.
+    abort = function(text) {
+      throw text;
+    };
+
+    try {
+      getWasmTableEntry($0)();
+    } catch(e) {
+      console.error('Threw an exception: ' + e);
+      return e.toString().includes('this function has been declared to only be callable from the main browser thread');
+    }
+    console.error('Function did not throw');
+    return 0;
+  }, func);
+  return threw;
+}
+
+void *thread_main(void *arg) {
+  REPORT_RESULT(might_throw(proxied_js_function));
+  return 0;
+}
+
+char stack[1024];
+
+int main() {
+  proxied_js_function(); // Should be callable from main thread
+
+  pthread_t thread;
+  pthread_attr_t attr;
+  pthread_attr_init(&attr);
+  pthread_create(&thread, &attr, thread_main, 0);
+}
diff --git a/test/test_browser.py b/test/test_browser.py
index 67bd81289a135..1def172ef1e8d 100644
--- a/test/test_browser.py
+++ b/test/test_browser.py
@@ -5272,6 +5272,20 @@ def test_wasm_worker_no_proxied_js_functions(self):
     self.btest('wasm_worker/no_proxied_js_functions.c', expected='0',
                cflags=['--js-library', test_file('wasm_worker/no_proxied_js_functions.js')])
 
+  # Tests that the proxying directives foo__proxy: 'abort' and foo__proxy: 'abort_debug' work.
+  @also_with_minimal_runtime
+  @parameterized({
+    '': ('1', ['--js-library', test_file('wasm_worker/proxy_abort.js')]),
+    'no_assertions': ('1', ['--js-library', test_file('wasm_worker/proxy_abort.js'), '-sASSERTIONS=0']),
+    'debug': ('1', ['--js-library', test_file('wasm_worker/proxy_abort_debug.js'), '-sASSERTIONS']),
+    'debug_no_assertions': ('0', ['--js-library', test_file('wasm_worker/proxy_abort_debug.js'), '-sASSERTIONS=0']),
+  })
+  def test_proxy_abort(self, expect_result, args):
+    self.btest('pthread/proxy_abort.c', expected=expect_result, cflags=args + ['-pthread', '-sPTHREAD_POOL_SIZE=1'])
+
+    self.set_setting('WASM_WORKERS')
+    self.btest('wasm_worker/proxy_abort.c', expected=expect_result, cflags=args)
+
   # Tests emscripten_semaphore_init(), emscripten_semaphore_waitinf_acquire() and emscripten_semaphore_release()
   @also_with_minimal_runtime
   def test_wasm_worker_semaphore_waitinf_acquire(self):
diff --git a/test/wasm_worker/proxy_abort.c b/test/wasm_worker/proxy_abort.c
new file mode 100644
index 0000000000000..49e4db7f2ac2b
--- /dev/null
+++ b/test/wasm_worker/proxy_abort.c
@@ -0,0 +1,38 @@
+#include <emscripten.h>
+#include <emscripten/wasm_worker.h>
+#include <assert.h>
+
+// Tests behavior of __proxy: 'abort' and __proxy: 'abort_debug' in Wasm Workers.
+
+void proxied_js_function(void);
+
+int might_throw(void(*func)()) {
+  int threw = EM_ASM_INT({
+    // Patch over abort() so that we can gracefully finish the test without
+    // an unhandled exception hanging the test.
+    abort = function(text) {
+      throw text;
+    };
+
+    try {
+      getWasmTableEntry($0)();
+    } catch(e) {
+      console.error('Threw an exception: ' + e);
+      return e.toString().includes('this function has been declared to only be callable from the main browser thread');
+    }
+    console.error('Function did not throw');
+    return 0;
+  }, func);
+  return threw;
+}
+
+void worker_main() {
+  REPORT_RESULT(might_throw(proxied_js_function));
+}
+
+char stack[1024];
+
+int main() {
+  proxied_js_function(); // Should be callable from main thread
+  emscripten_wasm_worker_post_function_v(emscripten_malloc_wasm_worker(1024), worker_main);
+}
diff --git a/test/wasm_worker/proxy_abort.js b/test/wasm_worker/proxy_abort.js
new file mode 100644
index 0000000000000..27e816e90b991
--- /dev/null
+++ b/test/wasm_worker/proxy_abort.js
@@ -0,0 +1,6 @@
+addToLibrary({
+  proxied_js_function__proxy: 'abort',
+  proxied_js_function: function() {
+  	console.log('In proxied_js_function');
+  }
+});
diff --git a/test/wasm_worker/proxy_abort_debug.js b/test/wasm_worker/proxy_abort_debug.js
new file mode 100644
index 0000000000000..59e4172c9a498
--- /dev/null
+++ b/test/wasm_worker/proxy_abort_debug.js
@@ -0,0 +1,6 @@
+addToLibrary({
+  proxied_js_function__proxy: 'abort_debug',
+  proxied_js_function: function() {
+  	console.log('In proxied_js_function');
+  }
+});