Brexiteer Jacob Rees-Mogg | Dan Kitwood/Getty Images Jacob Rees-Mogg denies MPs issued ‘ultimatum’ to Theresa May over customs partnership ‘We’re not in the business of making threats,’ says leading Brexiteer.

Tory MPs haven't issued an ultimatum to British Prime Minister Theresa May over her support for an ongoing "customs partnership" with the EU after Brexit, Brexiteer Jacob Rees-Mogg told BBC Radio 4 Wednesday.

Sources told the Telegraph that a group of MPs are considering withdrawing their support for the PM if she pursues a customs partnership with the EU, which would mean the bloc's customs arrangement would be mirrored at U.K. borders and Britain would collect tariffs for the EU. To bolster their case, the Brexiteers Wednesday released to the media a consultancy report they commissioned, which suggests a customs partnership would make the British international trade department "obsolete" and make it "impossible" to forge meaningful trade deals.

But Rees-Mogg, who leads the powerful European Research Group made up of around 60 Brexiteer Conservative MPs, told the Today program there is "no question" of the group having issued an ultimatum.

"We’re not in the business of making threats," he said, adding that the MPs are "very supportive of the prime minister." The report "is not a revolver, it’s not a dueling pistol," Rees-Mogg said.

The report was released ahead of a meeting Wednesday in which senior ministers will discuss different options for the post-Brexit customs relationship with the Continent.

A customs partnership is the option preferred by May, Chancellor Philip Hammond and Business Secretary Greg Clark, according to sources, because it will allow Britain to strike trade deals after Brexit while avoiding a hard border across Ireland.

The alternative being considered by May's inner Cabinet is the “highly streamlined customs arrangement,” which involves using technology solutions to lower customs barriers.

Brussels has already rejected both of the U.K.'s customs models.