BERLIN (Reuters) - Germany’s Social Democrats (SPD) are pushing for a vote this week to legalize gay marriage, capitalizing on a surprise shift from conservative Chancellor Angela Merkel three months before an election.

A reveller of the annual Christopher Street Day gay parade (CSD) holds a placard in Cologne, western Germany, July 5, 2015. REUTERS/Wolfgang Rattay

The issue became a hot election topic after Merkel’s three potential coalition partners, including her current SPD partners, made it a condition for sharing power, effectively forcing the conservative chancellor’s hand.

At an event hosted by women’s magazine “Brigitte” on Monday evening, Merkel said she had taken note of other German parties favoring same-sex marriage and would allow a free vote.

“I would like to lead the discussion more into a situation where it is a question of conscience rather than something I push through with a majority vote,” she said.

The move could antagonize some in her traditionally Catholic conservative bloc, some of whom oppose any change. Merkel has previously argued against same-sex marriage.

SPD leader Martin Schulz said on Tuesday his party would push for a vote in parliament this week, before the start of the summer recess.

“I hope our colleagues in the conservatives will cooperate,” he said, raising the pressure on his conservative partners - who want a vote after the election.

Schulz needs to make up ground for his center-left party in the election race and has sharpened his attacks on Merkel, but he made clear he would not end the coalition.

Merkel’s conservatives accused him of acting irresponsibly.

“That is a breach of trust,” said Volker Kauder, head of Merkel’s conservative bloc in parliament, adding the SPD’s behavior on such a sensitive topic showed it was “not suited to government”.

With broad support among Germans for gay marriage, the law would likely get easy approval in the lower house of parliament if conservatives could vote according to their conscience and not face a party whip.

Polls put Merkel’s conservatives 10-15 points ahead of the SPD, but short of a parliamentary majority.

The SPD, pro-business Free Democrats (FDP) and the Greens have made gay marriage, a step up from same-sex civil partnerships which have been allowed since 2001, a condition for a tie-up.

The LSVD association representing gays welcomed Merkel’s shift while describing it as a face-saving measure.

“After 15 years of an ideological blockade .. social pressure and the commitments of other parties have made an impact,” said LSVD spokesman Axel Hochrein. “Equal rights for all people is part of our constitution,” he said.