A number of Jeremy Corbyn's shadow cabinet could vote against triggering Article 50 in defiance of the leader's stated policy, reports claim.
Four shadow cabinet members and many junior frontbenchers have raised concerns about the legislation, which starts the process of Britain leaving the EU.
This is despite Jeremy Corbyn previously saying that Labour's support for triggering Article 50 is "unconditional."
If the Government loses its Supreme Court appeal, ministers are expected to table a bill on Wednesday seeking permission to activate Article 50 and begin the formal process of Brexit negotiations.
One Labour MP told The Guardian: “I’m concerned that if we wave article 50 through, my constituents will go crazy.”
Last year MPs voted in agreement with Theresa May's proposed timeframe for the negotiations, however 89 backbenchers opposed the idea.
Twenty-three of those were Labour MPs, despite Corbyn's pledge of support for Brexit. A further 23 Labour MPs abstained from the vote.
Theresa May has already guaranteed MPs a vote on the final deal she negotiates with Brussels, having made the promise in her keynote Brexit speech on Tuesday.
Concerns have been raised by some Labour MPs about the detail of Mrs May's speech, and some have expressed worry that Labour failed to mark out a position after her address, The Telegraph said.