Special forces are part of force Germany plans to deploy
The move follows a threatened rebellion against the deployment from within the Greens - the chancellor's coalition partners - and from within his own Social Democratic party.
The confidence vote is expected to be held on Friday - alongside a delayed vote on the deployment, which had been due to take place on Thursday.
Mr Schroeder announced last week that he wanted to send nearly 4,000 troops to join the US-led operation, a move which requires parliamentary backing under the German constitution.
The looming rebellion by some members of the Greens could also be joined by a number of Social Democrats, who say they have not yet decided whether to support the deployment.
Senior Social Democrat Gernot Erler said Mr Schroeder felt he had no option except the confidence vote.
"The Chancellor sees no other possibility," Mr Erler said.
Credibility
Even if Greens and some Social Democrats had rebelled on the deployment issue, Mr Schroeder would have had no trouble securing a majority, as the opposition Christian Democrats were backing the plans.
But Mr Schroeder is thought to have seen the potential rebellion as damaging to his coalition's credibility, forcing him to rely on opposition votes to push the policy through.
The issue of deploying troops to Afghanistan has proved divisive for the Greens themselves.
German Foreign Minister Joschka Fischer is a Green Party member who backs the campaign. But other senior leaders do not, along with many ordinary members of a party whose roots are in the pacifist movement.
The confidence vote will be only the fourth in Germany's post-war history.
Losing would leave Mr Schroeder with several options, including fresh elections, running a minority administration, or finding new coalition partners.