A lawyer and a trio of Green party politicians filed an Irish lawsuit seeking to give the U.K. a last-minute Brexit escape clause if public sympathy turns against leaving the European Union during two years of negotiations triggered last week.

Lawyer Jolyon Maugham, who has been a vocal Brexit opponent, filed the suit in Dublin Friday, according to an April 1 statement on Maugham’s website. He is seeking a declaration that Article 50 “is revocable at the discretion” of any EU member state, Maugham says in the case filings.

Theresa May’s March 29 notification of Article 50 initiated a two-year period permitting Britain to negotiate with the remaining member states on their future relationship. In a six-page letter submitted to EU President Donald Tusk, May formally began talks that will end with Britain breaking ties with its largest trading partner after more than four decades.

“We know that the United Kingdom can decide to remain if the other 27 member states give us permission,” Maugham said in the statement. “But can we withdraw the notification if our Parliament or, in a referendum on the final deal, the people of the United Kingdom decided that they wished to remain?”

Maugham is joined in the lawsuit by Northern Irish politician Steven Agnew, England and Wales Green Party co-leader Jonathan Bartley and Keith Taylor, a Green member of the European Parliament. The tax lawyer has said previously that his ultimate goal is to get the case referred to the EU Court of Justice in Luxembourg.

The government brushed aside the basis for Maugham’s claim, saying that there will be no backing out of Brexit.

“The people of Britain have expressed their will to leave the European Union,” said May’s spokesman, Greg Swift. “We’re going to get on with doing it.”

The lawsuit is the latest in a line of cases designed to complicate the Brexit path. Earlier this year, investment manager Gina Miller won a ruling from the U.K. Supreme Court that blocked May from triggering Article 50 without permission from Parliament.

Miller is also considering filing a new challenge in an attempt to clarify whether or not the government could legally enact the Great Repeal Bill, intended to enshrine EU law into U.K. statute when Brexit takes place.