If an employee resigns they must give the proper notice stated in their contract.
Or if they do not have a contract or a notice period is not set out in the contract the employee can give the minimum of 1 weeks' notice.
However, an employee is entitled to resign without giving any notice if the employer commits a serious breach of the employment contract.
See Employer's Breach
Forced Resignation
Where an employee is forced to resign, because the alternative would be dismissal by the employer, the employee can still claim Unfair or Wrongful Dismissal.
