Unions are set to win the right to expel members from unpopular political parties, it has emerged.
The forthcoming employment bill, previewed in the Queen's Speech, will bring union rules in-line with European legislation and grant them the right to expel members who are also members of parties such as the BNP.
The BNP has attacked the measure as "Stalinist".
The European Court of Human Rights has already ruled unions can expel members who are involved in political parties with views at odds with their stated aims.
Aslef, the train drivers' union, took the government to the European Court of Human Rights after it ruled it could not expel a member for belonging to the BNP.
The British government had until now opposed the exclusion of anyone who belonged to a legitimate political party.
Two employment tribunals in the UK ruled Virgin train driver Jay Lee could not be expelled from Aslef, despite standing as a candidate for the BNP in 2002.
The tribunals ruled unions could only expel members on the grounds of their conduct, not purely because they were members of a political party.
This was over-ruled by the European Court, however. It ruled Mr Lee would not suffer financially if he was expelled and pointed out he was free to join another union.
Notes for the employment bill say it will amend trade union membership laws "in light of the European court judgement in Aslef versus UK".
It clarified this will give unions the right to "expel members on the basis of their membership of a political party."
A spokesman for the BNP said the move was "vindicate, petty and a Stalinist way of going about things".
Speaking to politics.co.uk, he challenged the TUC to throw out any member that votes for the BNP, arguing that much of the BNP's support comes from the white working class.