The Transport and General Workers' Union has claimed the new law, which was introduced in July, falls short of international standards.

But the Employment and Social Security Committee said it will help resolve disputes more quickly.

Hundreds of union members demonstrated against the law in March.

In July, the law was condemned by the union's national conference in Blackpool.

Now the union will hold another rally in Royal Square on 27 September, and is calling for its members to make a stand.