Tensions have surfaced in Germany's new ruling coalition over how to handle migrants from Bulgaria and Romania.
Conservative Bavarian allies of Chancellor Angela Merkel say extra measures are needed to prevent "benefit tourism" in the EU.
But the foreign ministry, now run by the centre-left Social Democrats (SPD), warned that questioning freedom of movement was "harmful to Europe".
Bulgarian and Romanian workers are now free to get jobs anywhere in the EU.
Bulgaria and Romania, the EU's poorest countries, were subject to temporary labour market restrictions when they joined the EU in 2007. Nine countries kept the barriers in place until 1 January.