The campaign to get Britain out of the EU has been given a sizeable boost after one of the UK's most controversial and well-known trade unions voted to support a Brexit.
The RMT, which represents workers in the transport industry, made the move at its Annual General Meeting (AGM) in Newcastle.
Mick Cash, the general secretary of the union, claimed that the EU's policies are "at odds with the aspirations" of the organisation.
"EU policies are at odds with the aspirations of this union as the various treaties and directives are demanding the privatisation of our rail and ferry industries," said Cash.
"The EU is also secretly negotiating trade deals with the US and Canada which will decimate the health and education sectors and hand huge powers to transnational corporations over nation states and their governments."
The union is probably best known for its disputes with Transport for London and industrial actions affecting the London Underground, rather than its Eurosceptic position.
But the RMT's late leader, Bob Crow, was an outspoken critic of the 28-member bloc and attacked the EU from the left.
The union also campaigned in the No2EU-Yes to Democracy coalition in the run-up to the 2009 European Parliament elections alongside the Communist Party (UK).
The RMT will likely give the Out campaign a considerable lift ahead of the promised EU referendum by the end of the 2017.
The organisation is one of the UK's fastest growing unions at a time when union membership is generally in decline.
The number of people in a union between 2003 and 2013 dropped by 15.5% (7.7m vs 6.5m), according to House of Commons data. The RMT, in comparison, saw its membership surge by 15.7% (67,476 vs 80,105) over the same period.
The union will likely be joined on the left side of the Brexit campaign by Labour for Britain, a pressure group set up by Eurosceptic MPs Kate Hoey and Graham Stringer.
The freshly formed organisation, which is not calling for the UK to leave the EU at the moment, also has the support of John Mills, the founder of household goods firm JML, who gave Labour £1.6m ($2.5m) worth of shares last year.