The Houses of Parliament are seen through railings, in central London, Britain November 21, 2018. REUTERS/Peter Nicholls

LONDON (Reuters) - British Prime Minister Theresa May’s bid to win approval for her Brexit deal will have to overcome attempts to block or change it by rival lawmakers on Dec. 11, a proposed format for the debate published on Wednesday showed.

The government has set out the details of a debate on a motion to approve May’s plan to take the country out of the European Union, allowing for amendments to be discussed which could try to reshape the deal she brought back from Brussels.

The format of the debate has been keenly awaited to see whether rivals would have a chance to test their alternative exit plans, such as remaining in the EU’s customs union or making exit conditional upon a second referendum.

Any such amendments would not be legally binding on the government, but would prove politically hard to ignore.

May already has an arduous task to get the motion approved. It is opposed by a large group of lawmakers from her own party, the Northern Irish party that props up her minority government and by all opposition parties who say they will vote against it.

Defeat would likely unleash huge political uncertainty and could roil financial markets.

According to documents filed at Britain’s parliament on Wednesday, debates will be held on December 4, 5, 6, 10 and 11 with up to six amendments selected on the final day. The opposition Labour party said on Twitter the debate would conclude at 1900 GMT on Dec. 11.

The amendments could be put to several votes, meaning that as well as overcoming the huge opposition to her plan, May will have to defeat attempts to add extra conditions to it or to thwart the exit agreement altogether.

The government has previously voiced concerns that any of these so-called amendments that win support in the house of commons could prevent the government from ratifying the exit deal because the amended motion would not provide the necessary unequivocal approval required under previously passed legislation.