A senior German politician and key ally of chancellor Friedrich Merz has resigned as chair of the Christian Democrat (CDU) party after he and his husband used a surrogate mother to become parents, a practice he has criticised in the past and his party is vehemently opposed to.

Surrogacy is banned in Germany, a policy Jens Spahn refused to relax when he was health minister in 2020, so he and his husband, Daniel Funke, used a surrogate mother in the US.

After writing, in 2015, that “as a gay man and a Christian I find it personally very hard to warm to the idea of a rented womb”, Spahn welcomed the child on Wednesday, telling the German newspaper Bild: “Georg is our greatest joy. This feeling is almost impossible to put into words.”

The announcement immediately attracted criticism from people inside and outside the Christian Democrat party, with many levelling charges of hypocrisy at Spahn.

“Politicians who set standards for others must be measured by them too,” Marion Rosin, a Christian Democrat in Thuringia and part of the Women’s Union, told the BBC. “If that credibility is gone, resignation is a matter of consequence.”

Under the 1990 Embryo Protection Act, surrogacy in Germany is punishable with three years’ imprisonment or a fine, so many German couples opt for surrogacy pregnancies abroad.

In February, when the surrogate mother of Spahn’s child was around four months pregnant, the Christian Democrats (CDU) voted to maintain the ban at a party conference.

Spahn, 46, a prominent voice on the CDU’s rightwing flank who has been pushing for a more hardline stance on immigration, initially sought to defend himself in interviews with the media.

He told Bild he had “wrestled with myself for a long time, including on the issue of surrogacy” before the couple decided to go ahead.

But this failed to pacify his critics, including prominent members of his own party. “Jens Spahn is no longer tenable as chair of the parliamentary group and must resign,” Daniel Peters, the leader of the CDU in the state of Mecklenburg-Western Pomerania, told the Bild newspaper on Friday. He added it was “completely unacceptable” for Spahn to vote one way as a senior CDU politician and then “act quite differently as a private individual”.

Spahn’s party colleague and health spokesperson Janosch Dahmen also said the issue was about double standards and Spahn’s political credibility, not about his child.

“Anyone who advocates for rules politically should be able to explain clearly why those rules apparently do not apply to them personally,” Dahmen said.

As the calls for Spahn’s resignation mounted, Merz declined to comment on Spahn’s future in the party, telling reporters on Friday the issue would be discussed at the party’s next executive meeting.

That day, Spahn told Bild in an interview: “One thing is clear to me: For me, and this becomes clearer to me every hour, there is nothing more important than my family.”

On Saturday, Spahn resigned from his position in the party.

“In recent days, I have come to realise that my personal happiness in starting a family with my husband and becoming a father is incompatible with my political office,” Spahn said.

In a post on X, Merz described Spahn’s decision to resign as “right and inevitable. Credibility is the most valuable asset in politics,” he wrote.