EBay’s PayPal has begun restricting accounts of people it suspects of using the payment service to place bets on NCAA basketball championship tournament games, starting this week.

PayPal has sent alerts to some users who have used the service in connection with March Madness wagers, saying that their account use has been “limited.”

The user agreement for PayPal prohibits US account use for sending or receiving payments for “activities that involve gaming and/or any other activity with an entry fee and a prize.”

The alert asks the user to sign an online “Acceptable Use Policy affidavit” to regain full use of the account.

Bergen Kay, a spokeswoman for San Jose, Calif.-based PayPal, declined to comment on how the company’s system identifies alleged gamblers.