Denmark can put some constraints for ships passing the straits. They are danish water. So the Baltic is special in that you can’t reach it on international wate

Denmark can put some constraints for ships passing the straits. They are danish water. So the Baltic is special in that you can’t reach it on international water. Similar to the Black Sea. But these restrictions are codified in existing agreements so I don’t think Denmark could easily and unilaterally change them to include more conditions. But they could start enforcing ships following the existing requirements for environmental safety and insurance. It would make life pretty difficult for those shipping oil past the sanctions in rusty single hull tankers.