Hmm, I lived in California for a long time and companies definitely asked on a regular basis. Do you know when it was made illegal?

This depends entirely on where you are. This article is from last year, so it could have changed since then, but there is no federal prohibition on requesting your current pay in an interview, @AwkwardLookMonkeyPuppet@lemmy.world

For the lazy:

25. May a prospective employer ask me what I am currently paid or was paid in the past?

Effective January 1, 2018, Labor Code section 432.3 prohibits an employer from, either orally or in writing, personally or through an agent, asking any information concerning an applicant’s salary history information, which includes compensation as well as benefits. Furthermore, the law prohibits an employer from relying on an applicant’s salary history information as a factor in determining whether to offer employment at all or in determining what salary to offer.

That's a good new-ish law for California! I doubt people in most other states are similarly protected.