Ousted Catalan leader Carles Puigdemont attends the launch of a campaign for political platform "Junts per Catalunya" ahead of the December 21, 2017 Catalan regional election, in Oostkamp, Belgium, November 25, 2017. REUTERS/Yves Herman

BARCELONA (Reuters) - Pro-independence parties may fail to retain an absolute majority of seats in the Catalan parliament in regional elections next month, a poll published on Sunday showed, with pro-unity parties poised to increase their vote share.

Failure to win a majority in the regional parliament would be a blow for Catalan separatists who have billed the Dec. 21 election as a de-facto plebiscite on Madrid’s decision to impose direct rule on the wealthy region last month.

Following Spain’s worst political crisis in decades, the sacking of the secessionist Catalan government in October has a eased tensions for the moment, although victory for the pro-independence camp in December would plunge the northeast region back into uncertainty.

Catalan separatist parties are predicted to win 46 percent of the vote, down slightly from 47.7 percent in a previous election in 2015. Unionist parties combined would account for another 46 percent of votes, up from less than 40 percent last time, according to the poll by Metroscopia.

The poll shows pro-independence parties winning 67 seats, one short of the absolute majority they would need to retain control of the regional parliament.

Unionists forces would also fall short a majority in this scenario, although the poll suggests a high number of voters, around 23 percent, remain undecided.

The staunchly unionist center-right party Citizens looks set to cement its position as the largest opposition force with 25.3 percent of votes, gaining from the Catalan wing of Prime Minister Rajoy’s conservative Popular Party which drops to 5.8 percent and loses five of its 11 seats.

Turnout for the election, which former Catalan leader Carles Puigdemont said on Saturday would be the most important in the region’s history, is predicted to reach a record 80 percent.