Unfortunately, he may have found some sleezeball attorney who's willing to do this for a percentage of the "take". There are such animals out there in the zoo. So I'd say follow the good advice you've been given: Find an attorney (sometimes there are good ones who offer services through women's centers), get some preliminary advice, and collect documentation ... just in case. He may be bluffing, but you'll sleep better knowing you're prepared should he not be. The last thing you want is for your son to spend a summer with him while he's spending the child support money on booze. Better your son should see his dad only when he's sober.