An online petition calling for a second referendum on the U.K.’s membership of the European Union attracted the support of at least 2.5 million people late Saturday in London.

The petition to Parliament says: “We the undersigned call upon HM Government to implement a rule that if the Remain or Leave vote is less than 60 per cent or is based on a turnout less than 75 per cent there should be another referendum.”

In Thursday’s referendum, U.K. voters backed a so-called Brexit by 51.9 per cent to 48.1 per cent with a turnout of 72.2 per cent.

How such a change could be implemented retroactively by the government or lawmakers is unclear, even if there were any appetite for a new vote after a divisive campaign.

Parliament set no thresholds for participation in the legislation that set up the referendum, and the U.K. government ruled out a second vote during the campaign. Following the British vote to leave, European officials have said that the deal worked out with Prime Minister David Cameron to keep Britain in the EU is no longer on the table.

“The referendum has taken place; a decision has been made,” opposition Labour Party leader Jeremy Corbyn told reporters after a speech in London on Saturday. “I think you’ve got to accept that decision and work out our relationship with Europe in the future.”

That sense of finality was echoed by the U.K.’s most senior diplomat in Brussels, Jonathan Hill, who resigned as British commissioner to the European Union, saying, “what is done cannot be undone.”

The petition could trigger a debate among lawmakers. Any petition exceeding 100,000 signatures is eligible for discussion; Parliament’s Petitions Committee makes the final decision on whether to hold one, though such a debate never leads to a vote. In January, lawmakers debated whether to ban Donald Trump from the U.K. because of his comments about preventing Muslims from entering the U.S. It didn’t work: Trump visited Scotland Friday.

The petition has attracted the greatest level of support ever on the parliamentary website, exceeding the 587,000 signatures on the Trump motion. Out of the 10,735 petitions lodged on the government site, 27 have been debated since September 2015 with a further five awaiting debate, according to the website.

Read more about: