The leaders of Scotland, Wales and Northern Ireland’s pro-independence parties are set to meet in Cardiff on Monday to sign an agreement supporting independence referendums, bringing together political movements seeking major changes to the United Kingdom’s constitutional structure.

Scottish First Minister John Swinney of the Scottish National Party, Welsh First Minister Rhun ap Iorwerth of Plaid Cymru and Northern Ireland First Minister Michelle O’Neill of Sinn Féin are expected to sign the memorandum of understanding. The three leaders will attend the meeting as party leaders rather than in their official government roles.

The Cardiff meeting comes shortly after President Donald Trump said during his visit to Ireland that he would “love to see” Ireland unified. Speaking alongside Irish Taoiseach Micheál Martin in Dublin on Saturday, Trump said he believed reunification would eventually happen and suggested it “may as well happen now.”

Trump’s comments broke with the traditional approach of U.S. presidents, who have generally avoided taking a position on Northern Ireland’s constitutional future. The remarks also came as the British government continues to oppose holding a referendum on Northern Ireland’s status under current conditions.

The Northern Ireland Act 1998, which implemented key parts of the Good Friday Agreement, gives the British Secretary of State for Northern Ireland authority to call a border poll. Under the law, a referendum must be called if it appears likely that a majority of voters in Northern Ireland would support leaving the United Kingdom and joining a united Ireland.

The Cardiff Declaration would extend the independence push beyond Northern Ireland. Scotland rejected independence in a 2014 referendum by 55% to 45%, while the Welsh independence movement has gained greater political representation. Plaid Cymru became the largest party in the Welsh Senedd following the May election, according to the Institute for Government.

The coordinated meeting is also drawing opposition from unionist politicians in Northern Ireland. Democratic Unionist Party leader Gavin Robinson said Northern Ireland’s constitutional future should be decided by the people of Northern Ireland.

The three parties are expected to use Monday’s meeting to emphasize what they describe as their nations’ right to determine their own constitutional futures through democratic means. The declaration does not itself authorize any referendum, leaving the parties to continue pressing the British government for changes that would allow votes on independence or Northern Ireland’s constitutional status.