General secretary Paul Nowak said the union body will be lodging the case at the International Labour Organisation (ILO) because the legislation on ensuring minimum levels of service during industrial action “falls far short” of international legal standards.
Speaking on the opening day of the TUC Congress in Liverpool, Mr Nowak described the new law as “dreadful”.
Unions will attack the legislation during a debate on Monday, saying the new law is unnecessary and unworkable and will do nothing to resolve disputes.
The Government took forward the legislation following a year of unprecedented industrial action by hundreds of thousands of workers, including nurses, teachers, civil servants and railway staff.
Mr Nowak told a news conference in Liverpool: “The ILO has already slapped down the UK Government and ordered it to make sure existing and prospective legislation is in line with ILO standards.