Schroeder, who is trailing badly in opinion polls and has failed to get Germany's languid economy moving, said in May he would seek the vote after the latest in a bitter series of state poll reversals.
Although pollsters believe early elections could well put an end to his seven-year tenure, the embattled Schroeder has said he needs the vote to win fresh affirmation from voters.
His spokesman Bela Anda said this week that Schroeder had doubts about whether "he could have constant faith in a parliamentary majority for his policies".
He is on tricky constitutional ground and is expected in a speech before the Bundestag lower house to deliver an intricate defence of his decision to seek new elections via this route rather than, for example, resign.
Coalition deputies have been asked to abstain on Friday and Schroeder has said he will do the same, putting himself in the bizarre position of withholding support from his own government.
Opposition lawmakers, eager to take back the reins after seven years in the wilderness, will back the measure.
If President Horst Koehler agrees to dissolve parliament on the basis of the no-confidence vote and call elections in September, Schroeder will face a challenge from conservative opposition leader Angela Merkel, who aims to become Germany's first female chancellor.
President Koehler (L) will decide
whether to dissolve parliament
A poll by independent opinion research institute Forsa this week showed Merkel's Christian Union alliance with 47%support, versus 26% for Schroeder's Social Democrats (SPD).
Their junior coalition partner, the Greens, tallied 7%.
Meanwhile a new leftist alliance grouping former East German communists and SPD dissidents reached 11% support, creating a fresh complication for Schroeder.
The Christian Union's preferred coalition partner, the Free Democrats, scored 6%.
Although a vast majority of Germans hope the poll will be held this year - one year ahead of schedule - the move could still be thwarted by a court challenge.
Friday's vote is the second that
Schroeder has faced
Some coalition lawmakers, fearful of losing the election and bewildered by the request to express no-confidence in a government they still support, have said they are weighing an appeal to the federal constitutional court, Germany's highest tribunal.
But SPD leader Franz Muentefering said on Thursday that the party fully expected new elections and was arming for battle. "There is no plan B," he said.
Friday's vote is the second time Schroeder has faced a no-confidence vote before parliament.
In 2001, he called the vote to discipline members of the coalition opposed to committing German troops to the US-led war on terrorism after the 11 September 2001 attacks.
He won that by a thin margin.