The "Card Flagging" has happened in the past (actually many,many years ago), both with Visa and Mastercard (I have both) and its normally related to the banks policy as they are trying to protect your account against scammers.
All you need to do is call the bank and tell them to "KNOCK IT THE F***k OFF!!!" like I did.
Seriously,just call your banking institution. They can't tell you how to spend your money and legislation in the US hasn't been passed concerning online "Games" and the income it "may" generate.