Prime Minister Boris Johnson's Conservatives will complete Britain's exit from the European Union by the end of January and hold a budget in February if they win the national election.
Forman, along with Lucy Harris, and Annunziata Rees-Mogg - sister to Commons leader Jacob - announced the move in a shared video message on Thursday.
It follows the sacking of MEP John Longworth for criticising Nigel Farage for standing against the Conservatives in key seats.
"I haven't spoken to anyone about it - they wouldn't be able to bribe me".
"And I'll tell you something, Boris Johnson's deal unamended is unacceptable and I certainly stand by that".
The leader of Britain's pro-European Liberal Democrats has suggested she could work with the opposition Labour party to stop Brexit if it removed its leader in the event of a hung Parliament after next week's election.
Ms Rees-Mogg, MEP for the East Midlands and a former Conservative candidate, said: "We need a strong Leave-supporting government to deliver the Brexit 17.4 million voted for".
Mr Longworth, who has previously called on Mr Farage to only stand candidates in a small number of seats, said: "For those who want Brexit, Boris Johnson's deal is the only option available, Labour does not have a plan".
A furious Mr Farage quickly fired back, and said the party had already worked to help the Tories in securing a majority for leaving the EU.
"I'm not even sure who owns Chequers actually because I'm trying to work that out. We are receiving a great reception from disenchanted Labour voters and believe we have a good chance of winning in many seats".
Asked if it was a "cast-iron guarantee", Mr Johnson said: "The possibility you allude to simply will not happen".
Lawyers for the Jewish Labour Movement (JLM) said 70 Labour staffers past and present had given sworn testimony into an official inquiry by the Equalities and Human Rights Commission (EHRC) into anti-Semitism in the party.
"When this was put to me", he said, "the price of doing this is we wouldn't just stand down in Conservative seats, we would stand down in a whole load more seats".
"We introduced an appeals procedure to deal with it and we introduced an education process, so that party members understood the hurt that can be caused by anti-Semitic remarks or anti-Semitic behaviour". Get Me Out Of Here!