Is it legal for Citibank to refuse to combine my available credit in order to transfer a bigger balance?

I want to consolidate my available credit (two Citi credit card accounts) in order to take advantage of a balance transfer offer. Citi says that they will consolidate credit, but they'll only allow balance transfer amount on the available credit before combining. Is this legal? I don't recall getting a notice specifying this. Thanks!|||Legal? They're the lender, so they can set the rules.