Derek Simpson, joint Unite general secretary, has said that moves should be taken to overturn European legal cases that allow employers to undercut wages and conditions as part of resolving the dispute.
He was previously less keen to organise protests against these judgments than many European trade union leaders.
New Labour has said it might challenge European Union law.
But this is the same government that has pushed for more anti-union laws in Europe.
During submissions at European Court of Justice hearings known as the Viking case, the Finnish Seaman’s Union (FSU) was appealing against an injunction preventing strike action on the Viking ferry line.
The Labour government argued that strike action is not a fundamental right.
It was the only state out of 14 questioned to put this position.
In the Laval case in 2004, a Swedish trade union demanded that a Latvian company, Laval, which was building a school in the Swedish city of Vaxholm, pay Swedish wages and sign its migrant workers up to a Swedish collective wage agreement.
Laval refused and unions picketed the site, effectively forcing it out of the Swedish market.
Unsurprisingly, the British government actively took the side of the company in the case.