How can a contract be varied?

A contract can only be altered in the following ways:

• by agreement between the parties
• through a collective agreement where there is a provision in the worker’s contract for this to be incorporated (a reference in a collective agreement may not be enough)
• through an existing term which allows for a variation in working conditions eg flexibility
• by the employer giving proper notice to end the existing contract and offering a new one incorporating the new terms. If this happens, the termination will be a dismissal and, under the terms of the Employment Law 2003 may be an unfair dismissal. Under this law, the employee may not not accept the new terms and may leave and claim constructive dismissal.
• any changes must be given to the employee in writing within 4 weeks of the change. 

If an employer makes a change to a contract without following any of the above this could be a breach of contract.