Home to the business capital Frankfurt, the unanimous vote in Hesse to hold a new poll, tentatively scheduled for January 18, comes after four rogue SPD deputies withdrew their support earlier this month for a minority coalition government.
The uprising, which party leader Franz Müntefering called a "disaster," pointed up bitter divisions between leftists and centrists in the SPD, the junior partner in Chancellor Angela Merkel's grand coalition government.
The SPD candidate for state premier, Andrea Ypsilanti, had fought to form a hotly-disputed alliance with the Greens and the tacit support of the anti-capitalist Left party. The four rebel deputies in Hesse cited Ypsilanti's plans as the reason for their decision, noting that she had pledged during the election campaign not to work with the far-left.
Hesse has been in political limbo since a February state election when neither Merkel's ruling conservatives nor the SPD won a majority with their preferred coalition partner.
The latest fiasco comes with the SPD trailing far behind Merkel's Christian Union in the polls ahead of a general election next September. The party is also expected to suffer heavy losses in the new Hesse election.