Chancellor Angela Merkel's plans for a new coalition with the Social Democratic Party hung in the balance Saturday as the centre-left SPD began counting a postal ballot of its grassroots members on whether to accept the coalition terms, according to dpa. Suspense has been mounting this week in Germany, with the names of the next Merkel cabinet to be kept secret until Sunday, after the SPD vote is over. The SPD leadership has voiced confidence it will win a rank-and-file majority to ally with Merkel, despite initial fears among party radicals that there had been too many compromises with Merkel's conservatives. If all goes well for Merkel, she will be formally re-elected chancellor in the Bundestag on Tuesday, with her cabinet sworn in the same day. If the vote fails, Merkel's efforts at government formation would go back to square one. Her only other practical options would be to invite the reluctant Green Party into a coalition or to call a fresh election to break the deadlock. Merkel conceded SPD calls to: legislate a minimum hourly wage in Germany, which could raise pay for millions, especially in eastern Germany; lower the legal retirement age to 63 for some, but not all, Germans; and divert federal funds to the states and municipalities. All postal ballots received up to midnight Thursday will be counted at a disused postal sorting centre in the capital Berlin. The operation Saturday is highly mechanized, with machines to open the sealed ballots before they are tallied. The party has about 475,000 active members. The party has already opened the voter declarations returned with the ballots. SPD sources estimate about two-thirds of the members will have voted. The SPD referendum has no precedent in Germany. Normally the upper echelons of a party decide on their own whether to enter a coalition. A large number of invalid votes would embarrass the SPD, suggesting many of the centre-left party's members failed to understand and follow the voting instructions. Merkel met Thursday with SPD leader Sigmar Gabriel and Horst Seehofer, leader of the Bavaria-only conservative party Christian Social Union (CSU), for talks which Seehofer said were aimed at settling the cabinet appointments. Despite the secrecy, Gabriel is widely tipped to become economics and energy minister, while a former foreign minister, Frank-Walter Steinmeier, is expected to reclaim the post if the Social Democrats gain the portfolio. Wolfgang Schaeuble, Germany's 70-year-old finance minister, has been widely tipped to retain that post. Political scientists say Christian Democratic Union (CDU) leader Merkel is likely to distribute five ministries to figures from her own party, three to the CSU and six to the SPD. Counting the chancellor and her chief of staff, that would make a cabinet of 16. By agreement, the political parties - not the chancellor - are likely to have the final say on whom to appoint to their allocated ministries. The CDU/CSU alliance narrowly failed to win an absolute majority at the September 22 general election. Merkel's previous coalition partner, the Free Democratic Party (FDP), failed to be returned to parliament. Merkel is now running Europe's biggest economy with caretaker powers. She has negotiated a 185-page policy accord with the SPD and CSU setting out most of the details of what her cabinet will do for the next four years.