You can always say "NO". No one is preventing from saying it except you.
If you can finish your work, got lots of free time and dont mind doing more then go for it.
If you can't finish your work and you still need to assist others, at the end of the day your boss will only blame you for not finishing it because you didn't "NO" and accepted the task.

Lastly tell your boss your work takes pririoty, if you got time and can assist you will do. If you can't don't blame me for not finishing their work.

This post has been edited by FastRealm: Feb 6 2025, 01:26 PM