Britain wants to change the rules governing the free movement of people across the EU, Home Secretary Theresa May will tell European ministers.
Mrs May will speak in Brussels, ahead of the lifting of movement controls on Bulgarians and Romanians.
She says free access to labour markets must not be allowed to lead to "mass migration".
However, some countries have already vowed to defend what they regard as a fundamental EU principle.
EU justice and home affairs ministers will meet in Brussels on Thursday.