If you are using Asana in your company, you probably wish tasks wouldn’t be assignable on a public holiday.
This is not a feature that is available, and I can somehow understand why: each country has different public holidays, and companies using Asana across multiple countries probably have some specific rules as well, so it would hard to code something that pleases everyone and is easy to use at the same time.
That being said, I do have a workaround for you: search for all tasks assigned on a given public holiday, and notify the assignee they will probably have trouble doing this task on time and suggest they reschedule.
But you are not going to paste a comment on dozens of tasks by hand, correct? So here’s the trick: create a project called “Public holiday - Warning trigger” with a rule “New task added > Post a comment…”. You’ll be able to select tasks 50 at a time, and multi-home them into this project to trigger comments to be sent!
I hope this helps