Vice Chancellor Sigmar Gabriel has received support from his own Social Democrats as well as the Left Party for a center-left alliance. His call came in response to growing support for the populist right-wing AfD party.
Across several German media publications on Monday, members of the Social Democratic Party (SPD), as well as the Left Party, the successor to the East German communist party, said they backed Sigmar Gabriel's proposed alliance.
"The parties and social movements of the center-left spectrum should stand together against the swing to the right," Thorsten Schäfer-Gümbel, deputy SPD chairman, told German newspaper Bild.
"Social democracy barely has an absolute majority anywhere, so we want to close ranks with progressive forces and are also open to new social movements," Schäfer-Gümbel said.
Even Gabriel's deputy Ralf Stegner called for an alternative to the current Grand Coalition, which consists of Angela Merkel's Christian Democrats (CDU), their Bavarian sister party, the CSU, and the SPD.
"Health insurance, modern family policy, good work, pensions and education, as well as tax justice - all that just doesn't go hand in hand with the Union," Stegner told Bild.
Frauke Petry and the rightwing Alternative for Germany (AfD) has seen a surge in popularity in recent months
CDU fires back
Leading CDU politicians heavily criticized Gabriel's comments and accused him of pandering to the left-wing members of his party.
"I believe this is a desperate attempt to somehow get on his feet again," said Volker Bouffier, state premier of Hesse.
He added that an SPD, Left and Green alliance "would be bad for Germany."
"It is only about reaching the Chancellery - no matter with whom," CDU board member Jens Spahn said.
Response to right-wing support
The comments on Monday came just days after Gabriel called for an "alliance of all progressive forces" in Germany in response to the strengthening of the right-leaning parties.
The center-left parties must reflect in order "to overcome their notorious sullenness, vanities and divisions," the SPD leader wrote in a guest article for Der Spiegel magazine.
The populist right-wing party Alternative for Germany (AfD) has enjoyed a surge in support in recent months, with opinion polls suggesting that they now hold 12 to 14 percent of public support nationwide.
The AfD now holds seats in eight of the country's 16 state parliaments - and looks on course to claim national representation in next year's general elections.
After months of tensions with the CDU/CSU Union, particularly over Merkel's open-door immigration policy, both parties have blamed each other for rise of the AfD.
CSU leader and Bavarian Premier Horst Seehofer reportedly said that the CSU would launch its own election campaign if the CDU failed to reign in the AfD's rising popularity.
Unity over presidential candidate
Co-chairman of the Left Party Bernd Riexinger deemed Gabriel's proposal a "clear signal" and called on the vice chancellor to open direct talks with his party.
"Ahead of the 2017 federal elections, we should lead a camp-style election campaign with the SPD against the conservatives," Riexinger told the Passauer Neue Presse on Monday.
"A first step would be a red-red-green agreement on a joint candidate for the office of president," he said.
Although the president of Germany is officially neutral as head of state, it usually falls to Germany's parties to either agree on a unity candidate, or to field rival ones.
Current President Joachim Gauck announced earlier in June that he would not be running for a second term in the presidential office, leaving the way open for speculation as to who will be his successor.