Lee Cattermole and Andrea Dossena were both sent off against Hull City in a game Sunderland lost 1-0, while Wes Brown was dismissed as Poyet's men suffered a 2-0 defeat to Stoke City last weekend.
Brown's red card has since been overturned by the Football Association's disciplinary panel, but Poyet is concerned his squad are setting a worrying trend.
"I can assure you they (Cattermole and Dossena) know what they've done. That's very important," the Uruguayan told the Shields Gazette.
"They know there is a limit, and they need to be careful. I hope it never happens again, but we'll see.
"We all make mistakes, and there is no explanation why you do it. It happens in a split second. But if you do it every week, you've got a problem."
"When someone does something really, really stupid and it's repetitive, he doesn't have a chance with me," Poyet added.
"They need to be professional."
