A resolution said MEPs "contest with vigour the position taken by some European leaders who want citizens' right of free movement to be modified and curtailed".
The resolution called on member states not to discriminate against migrant workers on the "supposed grounds they abuse social security systems".
"No state making this charge has been able to produce the proof demanded by the European Commission," it added.
EU Justice Commissioner Viviane Reding told Parliament yesterday that freedom of movement must be defended at all costs as a core European value, with no exceptions.
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The issue has heated up sharply since Bulgarians and Romanians were given full rights on January 1 to free movement in the European Union, stoking claims in Britain and elsewhere they would take local jobs or sponge off the welfare system.
In response, Britain rushed through measures in December restricting access to unemployment handouts for new migrants but there was no large influx from Bulgaria or Romania.
"It is time to end this ridiculous debate in Britain, as in other member states," Romanian Conservative MEP Marian-Jean Marinescu said.