Cabinet ministers should "exercise their collective authority" and rebel against Theresa May's Brexit deal, said ex-Brexit Secretary David Davis.
The Prime Minister has proposed that a "provisional tariff regime" be set for the entire United Kingdom to remain in the Customs Union while solving the problem of the Irish border.
The Brexiters suspect that this could turn into a permanent situation that would restrict the freedom to negotiate trade agreements.
Davis wrote in the Sunday Times that the plan was "unacceptable."
"This is one of the most basic decisions the government has made in this day and age," he added.
The issue of the border between Northern Ireland and the Republic of Ireland is one of the last obstacles to a divorce agreement with Brussels, and the type of "backstop" is still being argued over the border for broader trade between Britain and the EU keeping open arrangement can not solve it.
The EU version, which would only bring Northern Ireland into line with the Brussels rules, was considered unacceptable by Ms May and the DUP.
Mr Davis said the government's negotiating strategy has "fundamental shortcomings" stemming from the "unwise decision in December to accept the language of the EU in dealing with the Northern Ireland border."
The negotiations continued this weekend between the United Kingdom and the EU ahead of an important meeting of EU leaders in the coming week to decide if an agreement can be reached.
Deal or no deal
On Saturday evening, the Süddeutsche Zeitung reported that an agreement had already been reached between Mrs. May and the EU, which would be announced on Monday.
But a source # 10 told the BBC that the report was "100% categorically untrue" and negotiations continued.
The paper said it had seen a leaked memo from EU negotiators to EU ambassadors saying "deal made."
DUP leader Arlene Foster warned the PM on Saturday to accept a "dodgy" deal with the EU.
Before a crunching Brussels summit on Wednesday, Ms. Foster said that Ms. May should not support a plan that would "effectively block Northern Ireland".
According to a leaked e-mail reported in the Observer, Ms. Foster is preparing for a no-deal Brexit.
However, more than three-quarters of NHS trusts have failed to prepare for the UK's exit from the EU, according to the People's Information's "Freedom of Information" campaign.
The group has also commissioned a YouGov survey of British doctors and nurses, who now say they will return another referendum with a margin of three to one, according to the survey.