The head of Germany’s center-left Social Democrats lobbied party members Tuesday to vote in favor of opening coalition talks with Chancellor Angela Merkel’s conservatives, amid strong opposition from grassroots members.

Martin Schulz made the rounds in the populous state of North-Rhine Westphalia, talking with party members to push for their approval at a party convention Sunday to open formal negotiations with Merkel’s Union bloc.

A rejection of talks would be a setback for both Schulz and Merkel, who has already failed to forge a coalition with two smaller parties.

The Social Democrats and the Union bloc, who have governed Germany in a “grand coalition” since 2013, suffered heavy losses in September’s national election.

In non-binding votes, Social Democrats in the smaller states of Berlin and Saxony-Anhalt have indicated they’ll vote against opening coalition talks, while party members in Brandenburg voted in favor.

In North Rhine-Westphalia Schulz met with party members in Dortmund before heading to the state capital Duesseldorf for similar meetings in the evening.

The Social Democrats in North Rhine-Westphalia aren’t planning any poll ahead of time on whether to approve the talks, the dpa news agency reported, but with about a quarter of the delegates to the Sunday convention their support is key.