Merkel, who leads the Christian Democrats (CDU), ceded the powerful Finance Ministry to the SPD in a coalition deal finally agreed on Wednesday, more than four months after a national election last September in which both blocs lost support, Yeni Safak reported.
"I think the cabinet formation, as it is now, is a political mistake," Christian von Stetten, a CDU lawmaker who represents business interests, told broadcaster ARD, adding that this applied in particular to giving up the finance portfolio.
Handing over the Finance Ministry shows the high price the conservatives had to pay to renew the 'grand coalition' with the SPD that has governed Germany since 2013, and secure Merkel's fourth term in office.
Mass-selling daily Bild said Merkel had sold out.
"Chancellor at any price," Bild wrote on its front page, adding that "Merkel gifts the SPD the government."
Under the coalition agreement, the SPD will retain control of the Foreign, Justice and Labour Ministries among others.
Merkel ally Julia Kloeckner was forced to defend the coalition agreement.
"We have kept our key promises from the election campaign," she told broadcaster Bayerischer Rundfunk, adding that "For families, there is significantly more support. We will keep the finances stable. There will be no new debts, but also no tax increases."