Only 20 percent of those surveyed by Forsa for weekly newsmagazine Stern said they would vote for the SPD, down from 23 percent last week.
That record low puts the Social Democrats only five percentage points ahead of their leftwing rivals the hard-line socialist party The Left, which improved to 15 percent.
Manfred Güllner, the head of pollster Forsa, said the latest plunge in support for the SPD was a “low point not considered possible until now” for one of Germany's two major political parties.
He said the Social Democrats had been hurt by the recent announcement their candidate for Germany's largely ceremonial presidency, Gesine Schwan, would try to gain the backing of parliamentarians from The Left. Many voters apparently considered that “her candidacy could be a signal for a nationwide cooperation with The Left party” despite denials from the SPD leadership that it will work with the socialists at the federal level.
The SPD's current coalition partners, Chancellor Angela Merkel's conservative Christian Democrats, improved one percentage point to 36 percent in the Stern poll. The pro-business Free Democrats and environmentalist Greens also improved one percentage point, rising to 13 percent and 12 percent respectively.