Have you ever quit a job due to personal ethics?

I found out last week my Boss is using a non-union contractor to update the office. We lease in a Union ONLY building. The specifics are in his lease. He says he doesn’t care because he’s saving a “ton” of money. It bothers me. I like to handle business on the up and up. I’ve left positions before due to ethical issues I disagreed with. This one seems minor but it’s bugging me. It seems arrogant to ignore your Landlord’s rules and I respect the individual who makes the effort to abide by the rules to get into the Union.
I’ve lost respect overnight but it could be a learning curve for the Boss. Everyone makes mistakes, right? I know no one person is perfect and I’ve broken rules I realized later were wrong.