diff --git a/action.yml b/action.yml
index cc7f1cd..e31ef60 100644
--- a/action.yml
+++ b/action.yml
@@ -67,8 +67,8 @@ inputs:
     description: ""
     default: ""
 
-  merge_registry_json:
-    description: ""
+  merge_existing_auth_json:
+    description: "if existing registry auth json in .docker/config.json should be merge into the final auth json"
     default: "true"
 
   squash_layers:
diff --git a/dist/index.js b/dist/index.js
index 152dc54..86361ff 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -62167,6 +62167,34 @@ function mergeArgRegistryAuthJson(registryAuthJson) {
   }
 }
 
+function mergeExistingDockerAuthJson(registryAuthJson, targetFile) {
+  if (!core.getBooleanInput('merge_existing_auth_json')) {
+    return;
+  }
+
+  if (!external_fs_.existsSync(targetFile)) {
+    return;
+  }
+
+  try {
+    const existingJsonStr = external_fs_.readFileSync(targetFile, {encoding: 'utf-8'});
+    const existingJson    = JSON.parse(existingJsonStr);
+
+    if (existingJson.auths != null && typeof existingJson === 'object') {
+      for (const key in existingJson.auths) {
+        if (existingJson.auths.hasOwnProperty(key)) {
+          registryAuthJson.auths[key] = existingJson.auths[key];
+        }
+      }
+    }
+  }
+  catch (e) {
+    console.log(`Failed to parse existing docker auth json in file: ${targetFile}"`);
+    core.setFailed(`Failed to parse existing docker auth json in file: ${targetFile}"` + e.message);
+    process.exit(1);
+  }
+}
+
 function writeRegistryAuthJson(registryAuthJson, targetFile) {
   external_fs_.mkdirSync(external_path_.dirname(targetFile), {recursive: true});
   const jsonContents = JSON.stringify(registryAuthJson, null, 2);
@@ -62450,7 +62478,9 @@ try {
     console.log('determined .docker/config.json location: ', dockerConfigFile);
   }
 
+
   const registryAuthJson = {auths: {}};
+  mergeExistingDockerAuthJson(registryAuthJson);
   addCiRegistryAuth(ci_registry, registryAuthJson);
   mergeArgRegistryAuthJson(registryAuthJson);
   writeRegistryAuthJson(registryAuthJson, dockerConfigFile);
diff --git a/src/action.js b/src/action.js
index 5f73805..d47a2ae 100644
--- a/src/action.js
+++ b/src/action.js
@@ -8,6 +8,7 @@ import {
   executeDockerBuild,
   isTrueString,
   mergeArgRegistryAuthJson,
+  mergeExistingDockerAuthJson,
   prepareDestinations,
   prepareDockerArgs,
   processAdditionalRegistries,
@@ -42,6 +43,7 @@ try {
   }
 
   const registryAuthJson = {auths: {}};
+  mergeExistingDockerAuthJson(registryAuthJson);
   addCiRegistryAuth(ci_registry, registryAuthJson);
   mergeArgRegistryAuthJson(registryAuthJson);
   writeRegistryAuthJson(registryAuthJson, dockerConfigFile);
diff --git a/src/lib.js b/src/lib.js
index e5483a9..08df9b2 100644
--- a/src/lib.js
+++ b/src/lib.js
@@ -60,6 +60,34 @@ export function mergeArgRegistryAuthJson(registryAuthJson) {
   }
 }
 
+export function mergeExistingDockerAuthJson(registryAuthJson, targetFile) {
+  if (!core.getBooleanInput('merge_existing_auth_json')) {
+    return;
+  }
+
+  if (!fs.existsSync(targetFile)) {
+    return;
+  }
+
+  try {
+    const existingJsonStr = fs.readFileSync(targetFile, {encoding: 'utf-8'});
+    const existingJson    = JSON.parse(existingJsonStr);
+
+    if (existingJson.auths != null && typeof existingJson === 'object') {
+      for (const key in existingJson.auths) {
+        if (existingJson.auths.hasOwnProperty(key)) {
+          registryAuthJson.auths[key] = existingJson.auths[key];
+        }
+      }
+    }
+  }
+  catch (e) {
+    console.log(`Failed to parse existing docker auth json in file: ${targetFile}"`);
+    core.setFailed(`Failed to parse existing docker auth json in file: ${targetFile}"` + e.message);
+    process.exit(1);
+  }
+}
+
 export function writeRegistryAuthJson(registryAuthJson, targetFile) {
   fs.mkdirSync(path.dirname(targetFile), {recursive: true});
   const jsonContents = JSON.stringify(registryAuthJson, null, 2);