Theresa May’s long-running battle with her divided Conservative Party took a potentially more dangerous turn, as one of her former ministers began assembling lawmakers to vote against her Brexit plans.

Euroskeptic Tories are angry that the prime minister wants to keep the U.K. closely tied to the European Union’s single market after leaving the bloc. Foreign Secretary Boris Johnson and Brexit Secretary David Davis both resigned in protest last week. Now Steve Baker, another Brexit minister who quit, is coordinating lawmakers on WhatsApp ahead of key parliamentary votes, according to a person familiar with the strategy.

Their first opportunity is the Taxation (Cross-Border Trade) Bill, which returns to the House of Commons on Monday, the person said. Leading pro-Brexit Tory Jacob Rees-Mogg, chairman of the European Research Group, has offered amendments to the legislation which have little chance of passing, but are intended as a show of the Euroskeptic group’s strength.

On Monday, it appeared May might be trying to put off the moment she finds out just how angry her party is. An official in her office said the government was considering accepting the amendments, meaning all Tories would likely support them.

“The Government unfortunately believes that Brexit is not a good thing in itself,” Rees-Mogg told the BBC’s “Sunday Politics” program, declining to comment on how many lawmakers he expected to vote for the amendments. “It seems to think it has to be tempered with non-Brexit.”

Leadership Challenge

May’s most immediate threat is being faced with an absolute number of hard Brexiters who oppose her — 48, for example, would be enough to trigger a leadership challenge — rather than defeat on the trade bill itself. On paper, only seven Conservatives need to rebel for that to happen, but Rees-Mogg said both the taxation bill and a trade bill due for a vote on Tuesday are “sensible overall,” and that he doesn’t expect the votes to go against the government.

Still, he warned that in the long-term, parliamentary arithmetic would force May to either change her Brexit policy or try to rely on opposition Labour Party votes — a strategy he said would “split” the Conservative Party.

The Telegraph newspaper reported that more than 100 lawmakers were in the WhatsApp group, which if true would amount to a considerable threat to May’s leadership.

Meanwhile Johnson’s first intervention since he quit was low-key, an article in the Telegraph urging the country to “believe in ourselves, to believe in the British people and what they can do, and in our democracy.” It didn’t suggest he was about to challenge May’s authority.

May Warning

Over the weekend, May warned her party to get behind her plan or “risk ending up with no Brexit at all.”

“I am not going to Brussels to compromise our national interest,” May wrote in the Mail on Sunday. “I am going to fight for it. I am going to fight for our Brexit deal — because it is the right deal for Britain.”

May’s Brexit blueprint calls for a new “common rule book” with the EU for trade in goods, which she conceded was a compromise. She told the BBC’s “Andrew Marr Show” on Sunday that it was the only option that could adhere to the 2016 referendum result while also protecting jobs reliant on manufacturers’ supply chains and ensuring no hard border between Northern Ireland and Ireland.

But critics argue it would leave Britain signed up to the bloc’s regulations, limiting options for trade deals with non-EU countries in the future. Even U.S. President Donald Trump weighed in, warning that too much regulatory alignment with the EU would “kill” a trans-Atlantic free-trade deal.

Second Referendum

It’s also not only the Brexiters that May has to watch for. Justine Greening, who resigned from the government in January, told the BBC that May’s plan satisfied no one and that a second referendum was needed to break the impasse.

“What we need is a clear route forward that settles this European question once and for all,” she said. Her proposal is a three-option referendum, where voters could choose between leaving the EU without a deal, leaving with the prime minister’s deal, or not leaving.

In her Mail on Sunday column, May warned parliamentarians on both sides of the Brexit argument that trying to scuttle the plan or seeking to change it risk causing “a damaging and disorderly Brexit.”

Adding to May’s woes, opinion polls show Labour opening up a lead over the Conservatives. A Deltapoll survey for the Sun on Sunday placed Labour at 42 percent, five points ahead of the Tories. According to an Opinium poll for the Observer, support for the Tories has dropped by six percentage points since the beginning of June to 36 percent, with Labour at 40 percent.

Foreign Office Minister Alan Duncan urged Tories to back May, and suggested “the economic cost and pain is likely to be very severe” if her strategy was blocked and the U.K. left the EU without an agreement.

“Any of those who think that they can either criticize her, challenge her or anything like that must realize that they are playing with fire and that they will end up destroying themselves,” Duncan said on Sky’s “Sophy Ridge on Sunday” program.