The announcement means that Andreas Norlén of the Moderate party is expected to be chosen as parliamentary speaker.
“Of the two nominated candidates from the Social Democrats and Moderates, we have made the active choice to vote for the Moderate candidate. We believe the Moderates are the party best-placed to lead a government in any constellation, given the parliamentary situation,” Sweden Democrat (SD) leader Jimmie Åkesson said in a statement.
The SD leader said that attempts had been made “as far as possible in this situation” to follow the tradition of giving the speaker’s position to the largest party in government.
Usually, the speaker is a member of Sweden's largest political party or bloc, meaning that after the September 9th election, a Social Democrat candidate would have been expected.
The role is a key one, as it is the speaker who puts a proposal for the new prime minister to parliament.
Åkesson’s party won 62 seats in the election, while the left and right of centre ‘blocs’ – party alliances led by the Social Democrats and Moderates – won 144 and 143 of the total 349 seats respectively in the Riksdag parliament.
Tobias Billström, parliamentary group leader with the Moderates, welcomed the announcement.
“We welcome broad support for Andreas Norlén in the parliament,” Billström told TT in a written message.
Of the smaller centre-right parties, the partners of the Moderate party in the so-called Alliance conservative bloc, the Christian Democrats also responded positively to the SD announcement. The Liberal party said it was “up to the SD” how they vote.
“They can vote as they wish. We cannot control how the Sweden Democrats vote,” Liberal party press secretary Eric Aronsson said.
On the other side of the parliamentary aisle, Left party leader Jonas reacted against the SD decision.
“I think this was expected. The Sweden Democrats and the Moderates are getting closer to each other politically. The immigration policy of the Moderate party is very much like that of the Sweden Democrats,” Sjöstedt told TT.
“If we get a Moderate government, that government would be completely dependent on the Sweden Democrats politically, and it is clear that is what the Sweden Democrats want,” he added.
SD’s influence on the choice of speaker would give the far-right nationalist party “indirect influence over the formation of government,” Green Party spokesperson Isabella Lövin told TT.
Those two parties still have the option of voting for a ‘cross-bloc’ speaker, thereby changing the outcome of Monday’s vote, Lövin said.
“Everyone who voted for the Centre and Liberal parties and who believed the promise that influence will not be given to the Sweden Democrats has been betrayed by this,” she added.
The Social Democrat candidate for parliamentary speaker Åsa Lindestam, whose candidature was announced on Thursday, will lose the vote on Monday provided no unforeseen developments occur.
The Social Democrats last week called for discussion on presenting a 'cross-bloc' candidate for parliamentary speaker, but the centre-right Alliance parties were not positive about the idea of a jointly proposed speaker.
After the election, which reduced the centre-left bloc's lead to just one seat, it remains unclear what Sweden's next government will look like and how any cross-bloc collaboration might take form.
READ MORE: The Local's coverage of the 2018 election