General secretary Dave Prentis addresses members of Unison Reuters

Britain's second largest union will launch a major consultation of its branches in March to determine how the 1.2 million-strong organisation campaigns ahead of the EU referendum. Unison will provide details for both sides of the Brexit vote to its members and the public services union will decide its position depending on the outcome of the exercise

"This could be to campaign to stay in Europe, campaign to come out or remain neutral and leave it up to members to decide," a spokeswoman for the union told IBTimes UK. Unite, which has more than 1.4 million members and, like Unison, is affiliated to Labour, will also likely make a decision on the EU referendum in March.

The union's executive council is still waiting on the agenda to be confirmed before their meeting. Unite has pro-EU policy but general secretary Len McCluskey has previously warned the union could back a Brexit if David Cameron sought to undermine workers' rights as part of his renegotiation deal with Brussels.

The Public and Commercial Services Union (PCS) will debate the referendum at its annual conference in May. A source close to the union told IBTimes UK that the body could repeat its position during the Scottish independence referendum in 2014, when the union remained neutral, quizzed both camps and let its 262,000 members decide for themselves.

A spokesperson for the Royal College of Nurses, which has more than 429,000 members, said the union also has a neutral stance on the vote, whereas rail unions the Associated Society of Locomotive Engineers and Firemen and the Rail, Maritime and Transport (RMT) workers are campaigning for a Brexit at the historic ballot.

The 20,000-strong Transport Salaried Staffs' Association, however, is expected to back a pro-EU position alongside the GMB Union. A source close to the union said the move would be a reluctant one as Cameron had "poisoned the well" with his controversial Trades Union Bill. The draft legislation, among other things, would enforce a minimum strike ballot turnout threshold of 50%.

Frances O'Grady, the general secretary of the Trades Union Congress, has also backed Britain staying inside the EU. "A Brexit would have massive implications for jobs, rights, and the very fabric of the UK," she told Reuters in January.

"If you take that floor away, workers will be worse off. It's a hell of a gamble for those, who want to leave Europe, to depend on particularly the government we have now to protect the rights on which so many people's working lives depend."

The Fire Brigades Union's executive council will discuss the issue during a meeting March, where it will be decide whether the matter will be raised at the union's annual conference in May. The organisation is set to reaffiliate with Labour after Jeremy Corbyn secured a victory at the party's leadership election in September 2015.

Cameron has not yet set a date for the EU referendum as he continues his renegotiations with Brussels, but the ballot is expected on 23 June.

The latest telephone poll from ComRes for ITV put "remain" eight points ahead of "leave" (49% versus 41%). But the survey, conducted between 11 and 17 February, showed that the gap between the positions had narrowed when compared to January.