Brake shoes may freeze to the brake drums if your brakes were warm and damp when you parked.
Deal with this situation slow and easy, just like almost everything else in winter driving. Release both the tractor and trailer emergency brakes.
Then push on the service brakes. This can put up to 1800 foot- pounds of pressure on the brake drums – a lot more pressure than anyone could manage with a hammer. Push down and release the service brake several times. This should clear the ice. Try moving forward in a small serpentine. Watch your trailer tires as you do this to make sure they are rolling. If they are not, set the emergency brakes again and release. Keep working with applying service and emergency brakes until the ice between the brake drum and lining breaks free.