If the problem cannot be resolved amicably, the matter may go to an industrial tribunal. Industrial tribunals make sure that employment laws are properly adhered to by employees and employers. They are made up of people outside the workplace who listen to the employer's and the employee's point of view and then make a judgement about the case. People can ask their union to represent them at industrial tribunals. Most cases that go to industrial tribunals are about pay, unfair dismissal, redundancy or discrimination at work.
Unions also offer their members legal representation.
Normally this is to help people get financial compensation for work-related injuries or to assist people who have to take their employer to court.