The opposition decided during its first post-election meeting to discuss presenting a motion to parliament to set a 2013 exit date for Swedish troops now stationed in Afghanistan, Swedish media reported.
"We are standing by the agreement we made and we are going to act on it in
parliament," Social Democrat and opposition leader Mona Sahlin told reporters.
Swedish parliament reconvenes next week for the first time since the September 19th election, when Reinfeldt is also scheduled to present his government.
The prime minister's four-party coalition won most votes in the September 19th general elections but fell two seats short of a majority of the 349 seats in parliament.
The ruling coalition has said it wants to extend the Swedish mission in Afghanistan and has refused to set an exit date for troops.
It has more seats than the opposition, made up of the Social Democrat, Green, and Left parties, but the anti-immigrant Sweden Democrats, which are not associated to either bloc, could play kingmaker on the issue.
The far-right, which was voted into parliament for the first time and holds 20 seats, has said it is opposed to Sweden's presence in Afghanistan and could very well vote with the opposition on the issue, although it has not yet said it would do so.
The presence on the far-right in parliament could also make Monday's vote of a new house speaker chaotic, media reported.
According to the reports, the Sweden Democrats have said they would support a speaker from the centre-right coalition, but only if the party gets a deputy speaker post.
Reinfeldt has vowed not to cooperate with the far-right, anti-immigrant Sweden Democrats and has instead said he will seek support from the Greens to pass legislation.
According to the opposition, he will opt to lead a minority government instead of building a new coalition, but he has not spoken publicly since the day after the election.