Britain’s Liberal Democrats opened the door to another coalition government with Prime Minister David Cameron’s Conservatives on Tuesday when party officials told they Financial Times they could support a referendum on the country’s European Union membership.

While Cameron has promised such a vote if he is reelected in May, the Liberal Democrats’ official position is that a referendum should only be called if additional powers are transferred to Brussels. Cameron, instead, wants powers back to curtail labor migration from other European Union states.

Nick Clegg, the Liberal Democrat leader and deputy prime minister, softened his stance on Monday when he refused to rule out a referendum altogether.

An ally of Clegg told the Financial Times that if the Conservatives insisted on “doing something so monumentally stupid” as calling an in-our referendum, “they will have to be extremely generous and persuasive.” The liberals would want a say in how the question is put to the British electorate and demand that non-citizens from European countries living in Britain as well as under-eighteens get a vote.

A Liberal Democrat minister said, “Those groups both got a vote in the Scottish referendum. I think they would expect a vote if there was also one on our membership of the EU.”

European Union citizens are allowed to vote in European and local elections in the country where they reside but do not get a vote in general elections. “Giving them a say on Britain’s membership of the EU is likely to prove controversial,” according to the Financial Times.

The United Kingdom Independence Party in particular could be critical of such a decision when Cameron suggested the referendum in the first place to woo Euroskeptic voters.

There are 2.7 million people living in Britain who were born elsewhere in the EU, according to the latest estimate by the Office for National Statistics. Not all of these will be foreigners, nor will all be voters, but this could still prove a powerful bloc in a tight race.

Recent YouGov poling suggest between 42 and 45 percent of Britons would vote to stay in the European Union while between 34 and 38 percent wants out.

The Liberal Democrats are projected to lose more than half of their 56 seats in the House of Commons but would still be needed to bring the Conservatives closer to a majority.

Neither the Conservative Party nor Labour — which has criticized the referendum proposal — is expected to win an outright majority.