LONDON     -   Two British opposition parties on Sunday proposed an even earlier election date than Prime Minister Boris Johnson has offered, trying to force his government to delay a final decision on its European Union divorce deal.

The chess move by the Liberal Democrats and Scottish National Party reflects the volatile political landscape now in Britain.

The ruling Conservatives desperately want a new election to bolster their numbers in Parliament, but they face resistance from the main opposition Labour Party, which fears the country will be unwittingly tricked into crashing out of the European Union without a deal.

The latest election proposal is an effort to force Johnson to delay debate in Parliament on his Brexit withdrawal bill until after any election, depriving him of a possible victory on his trademark issue going into the campaign. It makes Johnson’s government choose between holding an election to improve its position in Parliament and its goal of securing Brexit before that election takes place.

“The challenge is absolutely on (the prime minister), because if he is serious about wanting an election and if he’s genuine about having an election before Christmas, then he can back this bill,” Liberal Democrat leader Jo Swinson told the BBC on Sunday.

Looming over the political maneuvering is what Johnson and Parliament are going to do about his Brexit deal and how long extension EU leaders will give Britain to the current Brexit deadline, which is Thursday. The EU in principle has backed extending the Brexit deadline but officials were meeting again this week to figure out how long it should be.

The Liberal Democrats and the SNP plan to introduce legislation on Tuesday that calls for an early national election on Dec. 9, three days earlier than Johnson proposed and years earlier than Britain’s next scheduled vote in 2022.

Because U.K. law requires Parliament to be dissolved 25 working days before an election, the date of any poll will dictate how much time is available to debate Johnson’s Brexit withdrawal deal.

The Liberal Democrats expect a vote on their proposal Thursday, just days before Parliament would be suspended. That would effectively leave no time for lawmakers to consider Johnson’s Brexit deal.

In contrast, Johnson announced last week he will ask lawmakers on Monday to authorize a Dec. 12 election, then use the rest of the legislative term to push through his Brexit deal. Under this plan, Parliament would be dissolved on Nov. 7, giving lawmakers about seven days to debate the withdrawal agreement that Johnson and EU leaders agreed upon.

The two sides have effectively been debating Britain’s departure from the 28-nation bloc — which has never seen a member leave — since British voters in June 2016 chose to leave the EU. But Johnson’s deal was cemented only 10 days ago — and British lawmakers fear rushing through a document that has enormous economic and political consequences for the country.

The problem for Johnson is that his proposal requires a two-thirds vote of the House of Commons and it is opposed by opposition parties who fear it could lead to an economically damaging no-deal Brexit.

In contrast, the Liberal Democrat plan only needs a simple majority in the 650-seat House of Commons due to laws governing elections.