The majority of planned operations and all out-patient appointments at Neath Port Talbot, Morriston, Princess of Wales Hospital in Bridgend and Singleton Hospital have been cancelled.
An ABM spokesperson said: "In view of the prediction of freezing temperatures for the rest of the weekend we have decided to cancel the majority of operations that were planned and all out-patient appointments at all our hospitals.
"We will be concentrating on making sure we can staff our emergency and urgent care services safely during this period.
"Also, we will need to review our planned services for Monday depending on how the weekend progresses. We apologise for any disruption and thank our staff for their commitment and efforts in getting into work despite the adverse weather."