Bob Crow says the EU and business are driving the sell-off of the NHS
The UK is "sleepwalking" to privatisation of the NHS by Brussels, the left-wing No2EU - Yes to Democracy alliance has claimed.
The party said a recent extension of European internal market rules to cover healthcare paved the way for private companies to take over the NHS.
Leader Bob Crow said anyone who believes in "the NHS and public services should be voting No2EU".
The party says it opposes the "EU gravy train" and backs workers' rights.
Mr Crow - who is also general secretary of the RMT union - said the European Commission's Health Services Directive would mean "the break up of the National Health Service, which is being driven by the EU and their backers from the banks and big business".
No2EU, which opposes the Lisbon Treaty and campaigns to for UK withdrawal from the EU, staged a protest at the Department of Health in London.
The party argues that a succession of EU directives and rulings by the European Court of Justice have undermined workers' collective bargaining and the right to strike.
If elected, the party says its MEPs would refuse to take their seats in the the European Parliament in protest at the institution's "undemocratic" nature.
No2EU spokesman Brian Denny said the party's arguments had been well-received on the doorstep by voters from across the political spectrum, but blamed the media for not allowing them to get their message across.