No no no. It's even illegal to ask in a lot of states in the US. I know it is here in Washington at the least. Check in with regulations in your area and know your rights ahead of time.
Some other good responses:
"I'd rather not share that right now, I'd prefer to focus on the value that I can add to your company and this offer"
"I have an ethical concern with disclosing how my current employer compensates their employees, so I can't share that information with you"
The last one I would withhold unless they're being pushy, since it can come across overly strong in certain situations. It's a great one though, since the recruiter would have to knowingly ask you to compromise your ethics to get you to respond, and if that's the case that would be a good sign to look elsewhere.
I am not aware of any law prohibiting recruiters from asking your current salary in Washington state. (Perhaps you mean DC, but just throwing this out there.) California definitely made the question illegal since it unfairly disadvantages women who are typically paid less than male counterparts in the same role. All states should adopt such legislation.
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