MPs will be deciding whether or not they want to back the terms of the Prime Minister's negotiated deal.
Alex Cunningham, a Christian and the Labour MP for Stockton North, explained on Premier's News Hour why he feels forced to vote out of sync with many of his constituents.
"Well the people in my constituency - when they voted they liked the idea of the extra money for the NHS - the £350m a week. They had issues with immigration and freedom of movement...but above all, I think they were hoping that they would get something better out of the Brexit deal.
"That's not going to happen...what's on the table actually puts us in a worse position than we would have been if we just remained members of the EU.
"So I think at this stage we've got to reject it and the Labour party's position and my own personal position is we should be getting a Labour government. So we should have a general election and failing that, we should put the matter back to the people."
Mrs May has insisted she's secured valuable assurances from the EU on her Brexit deal - including on the Irish backstop.
In a speech in Stoke this morning, she warned MPs the public's faith in democracy is at stake - if they vote down her Brexit deal tomorrow.
She also said not leaving the EU is now more likely than a no-deal exit even though there's never been a referendum in the UK where the result has not been honoured.
However, Mr Cunningham said that was "nonsense".
He added: "I do think that the Prime Minister has probably done her best but she hasn't even bothered to talk to the MPs across the house or others over the two and half years she's been negotiating.
"I think it's a little bit late so I think we need somebody else to negotiate on our behalf."
He added that his constituents voted 2:1 to leave the EU, "so that makes life quite difficult for me because I'm going to disappoint a lot of them tomorrow because I will be voting against the deal proposed by the Prime Minister.
"And I will be doing my best to make sure that we also pass a vote to ensure that we don't end up with a no-deal Brexit as well."
He said he would be praying for the country ahead of the vote.
"I suppose the prayer for me is unity in our country and that we can eventually come up with a solution for this problem," he said.
"Whether that solution is a different sort of deal and we leave the EU or whether it's a deal that isn't possible and we actually remain. I think there's plenty for Christians to concentrate on in this period of time."
Listen to Alex Cunningham MP speaking to Premier's Eno Adeogun: