diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index bf630b7..979a257 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -11,6 +11,36 @@ concurrency:
   cancel-in-progress: false
 
 jobs:
+  tests:
+    name: test code
+    runs-on: "ubuntu-latest"
+    if: github.event.pull_request.title != 'relock w/ conda-lock'
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: conda-incubator/setup-miniconda@v3
+        with:
+          python-version: 3.11
+          channels: conda-forge
+          channel-priority: strict
+          show-channel-urls: true
+          miniforge-version: latest
+
+      - name: install deps
+        shell: bash -leo pipefail {0}
+        run: |
+          conda install --yes \
+            click \
+            ruamel.yaml \
+            conda \
+            conda-lock \
+            pytest
+
+      - name: run tests
+        shell: bash -leo pipefail {0}
+        run: |
+          pytest -vvs test_relock.py
+
   tests-lock:
     name: test updates
     runs-on: "ubuntu-latest"
diff --git a/action.yml b/action.yml
index 914c79d..571ff36 100644
--- a/action.yml
+++ b/action.yml
@@ -15,7 +15,13 @@ inputs:
     required: true
     default: 'conda-lock.yml'
   ignored-packages:
-    description: 'comma-separated list of packages whose version changes are ignored when relocking'
+    description: 'comma- or newline-separated list of packages whose version changes are ignored when relocking'
+    required: true
+    default: ''
+  include-only-packages:
+    description: >
+      comma-or newline-separated list of packages to exclusively include when relocking, all others will be ignored,
+      ignored-packages is applied to this list
     required: true
     default: ''
   relock-all-packages:
@@ -94,6 +100,7 @@ runs:
           --lock-file=${{ inputs.lock-file }} \
           --ignored-packages=${{ inputs.ignored-packages }} \
           --relock-all-packages=${{ inputs.relock-all-packages }} \
+          --include-only-packages=${{ inputs.include-only-packages }} \
           > ${{ github.action_path }}/summary.txt
         {
           echo 'summary<<EOF'
diff --git a/relock.py b/relock.py
index 428cc5b..bb9c3aa 100644
--- a/relock.py
+++ b/relock.py
@@ -13,6 +13,16 @@
 yaml.default_flow_style = False
 
 
+def _split_package_list(package_list):
+    packages = []
+    for line in package_list.split("\n"):
+        for pkg in line.split(","):
+            _pkg = pkg.strip()
+            if _pkg:
+                packages.append(_pkg)
+    return packages
+
+
 def _lock_to_ver(lock, platform):
     pkg_to_ver = {}
     for pkg in lock["package"]:
@@ -44,11 +54,18 @@ def _reformat_lockfile(lockfile):
 @click.option("--lock-file", required=True, type=click.Path())
 @click.option("--ignored-packages", required=True, type=str)
 @click.option("--relock-all-packages", required=True, type=str)
-def main(environment_file, lock_file, ignored_packages, relock_all_packages):
+@click.option("--include-only-packages", required=True, type=str)
+def main(
+    environment_file,
+    lock_file,
+    ignored_packages,
+    relock_all_packages,
+    include_only_packages,
+):
     relocked = False
     with tempfile.TemporaryDirectory() as tmpdir:
         try:
-            ignored_packages = [pkg.strip() for pkg in ignored_packages.split(",")]
+            ignored_packages = _split_package_list(ignored_packages)
             relock_all_packages = relock_all_packages.lower() == "true"
 
             have_existing_lock_file = os.path.exists(lock_file)
@@ -101,6 +118,8 @@ def main(environment_file, lock_file, ignored_packages, relock_all_packages):
                     for platform in envyml["platforms"]:
                         for pkg in new_platform_pkg_to_ver[platform]:
                             deps_to_relock.add(pkg)
+                elif include_only_packages:
+                    deps_to_relock = set(_split_package_list(include_only_packages))
                 else:
                     deps_to_relock = set()
                     for _spec in envyml["dependencies"]:
diff --git a/test_relock.py b/test_relock.py
new file mode 100644
index 0000000..2a2e192
--- /dev/null
+++ b/test_relock.py
@@ -0,0 +1,19 @@
+from relock import _split_package_list
+
+import pytest
+
+
+@pytest.mark.parametrize(
+    "input,output",
+    [
+        ("", []),
+        ("\n,\n\n", []),
+        (",", []),
+        ("\n", []),
+        ("conda", ["conda"]),
+        ("conda,python", ["conda", "python"]),
+        ("\nconda, python\nblah,blah\n,\n\n", ["conda", "python", "blah", "blah"]),
+    ],
+)
+def test_split_package_list(input, output):
+    assert _split_package_list(input) == output