Leaders of Germany's governing conservative parties are holding separate meetings to mull their next steps in a dispute over migration that has escalated into a threat to Chancellor Angela Merkel's government.

Interior Minister Horst Seehofer is calling for Germany to turn back at its border migrants previously registered as asylum-seekers in other European countries. Merkel opposes unilateral action, arguing it would weaken the 28-nation European Union.

Seehofer heads the Bavaria-only Christian Social Union, the sister party to Merkel's Christian Democratic Union.

A CSU leadership meeting Monday in Munich is likely to authorize Seehofer to go ahead with his plan — but it's unclear at what point. If Seehofer actually implements it in defiance of Merkel, it could threaten the future of the government and the chancellor.