STOCKHOLM (Reuters) - Sweden’s ruling Social Democrats launched their election manifesto on Tuesday promising an extra week of holiday for parents as the party seeks to avoid its worst showing ever in a national vote.

Polls show the Social Democrats remain Sweden’s biggest party, but their support has slumped since 2014 when they took power in a minority coalition with the Greens.

Swedes already enjoy a statutory five weeks of vacation a year for full-time employees as well as long parental leave, making them the envy of many in Europe.

“It is hard for many workers to take time off when schools are on holiday or when kids have study days,” the Social Democrats said in a statement.

“That’s why we want to give more help to parents who work.”

The plan, which will cost 5.4 billion Swedish crowns ($590 million) annually, will mean parents will be able to take 5 extra days a year of leave if they have children aged between 4 and 16.

Prime Minister Stefan Lofven has promised 35 billion Swedish crowns extra for welfare services over the next four years as well as more spending on the police and the military.

The Social Democrats have around 25 percent support in polls, ahead of the Moderates and Sweden Democrats.

In 2014, the Social Democrats got 31 percent.

Neither the center-left bloc, which includes the Greens and Left Party, nor the four-party centre-right Alliance looks likely to get a majority.

However, complex political maneuvers mean Moderate leader Ulf Kristersson is the bookies’ favorite to become the next prime minister.

To do that, he needs at least the passive support of the Sweden Democrats, a party with roots in the neo-Nazi fringe and which has around 20 percent support. Kristersson has ruled out a formal deal, which would split his own party and the Alliance.

But he could become prime minister even so if the Sweden Democrats back a parliamentary vote to dismiss Lofven after the election - which is likely - and abstain on a vote on his candidacy.

Sweden election graphic: tmsnrt.rs/2LmSZFD

($1 = 9.1511 Swedish crowns)