Getting a second job without your first employer knowing

Hey, I have a question regarding this. At some other threads, people say that we have to show a confirmation letter from the first employer stated they let us to accept the second employment. Is this true?

I am a full time staff in a company, working as an International sales. Currently thinking to do a part time at a university as a Research Assistant.

Ask the Ministry of Labor. I don’t think you are required to inform your primary employer about additional part time work, but my recommendation is to ask the people who know for sure.

Somebody else here might know for sure.