Occasionally disagreements do occur and the two sides cannot agree. In these cases the union may decide to take industrial action. Industrial action takes different forms. There are strict laws which unions have to follow when they take industrial action. A strike is only called as a last resort.
Strikes are often in the news but are rare.
Both sides have a lot to lose. Employers lose income because of interruptions to production or services. Employees lose their salaries and may find that their jobs are at risk. ACAS press releases are published on the Internet.