Andy Burnham has called for a separate "Labour Yes" campaign ahead of the referendum on the UK's membership of EU, putting the Leigh MP a step ahead of his leadership rivals on the issue.
The pro-EU push comes after Burnham was the first candidate to back the historic vote (in contrast to Labour's pre-election policy).
The shadow health secretary followed the move up by calling on David Cameron to hold the referendum in 2016.
Burnham will travel to Brussels today to meet Labour MEPs and Ivan Rodgers, the UK's ambassador to the 28-member bloc.
The 45-year-old will argue the case for a separate "Labour Yes" campaign in a bid to differentiate his party from the Conservatives.
The move would come after the parties canvassed under the "Better Together" banner in the run-up to the Scottish independence referendum last year.
"Even though Labour is in a leadership campaign, I am not going to let the EU debate be defined by Cameron," Burnham said.
"Today, I will discuss with Labour colleagues in the European Parliament what a distinctive pro-European reform package will look like."
"These are areas that David Cameron will not be focusing on and that is why we be raising them today to make the Labour case for Europe. Re-negotiation cannot be a green light to turn the clock back and weaken employment rights.
"Labour will also learn the lessons of the Scottish independence referendum and it is my intention to have a separate 'Labour Yes' campaign."
Labour leadership race
Mary Creagh, Yvette Cooper and Liz Kendall are also running to become Ed Miliband's successor, but so far Burnham is the only candidate to secure the required support of at least 35 MPs.
Cooper is close to the line with 31 signatures, Kendall has 21 and Creagh is well behind with just six.
Burnham was given another boost yesterday when the number MPs publicly supporting him hit 51 after 16 Labour representatives announced their support.
Kate Hoey, one of the new supporters, is seen as a Eurosceptic and a major Labour donor suggested that the Vauxhall MP could lead the "No" campaign ahead of the EU referendum.
John Mills, the founder of JML and a funder of the Business for Britain campaign, told The Guardian: "She knows her own mind, she is a tough fighter, and she has been around for a long while. She is a reliable cogent figure.
"These are very important qualities that you need in somebody who is going to lead a campaign like this."
Meanwhile, Cameron travelled to Germany, Poland, France and the Netherlands last week to press his case for EU reform.
The prime minister seemed to make some headway with German Chancellor Angela Merkel, who said she wanted to find a solution.
Ewa Kopacz warned that her compatriots and other EU citizens in the UK could be discriminated against if Cameron stop them from receiving in-work benefits.