Yes, employers can make changes to an employee’s work pattern however each case is unique. The employer might already have the power to make the change. Alternatively, it might seek an agreement with the employee that the change be made. At the other extreme, an employee might terminate the existing employment relationship and seek to re-hire on new terms - however this is not without considerable risks.
The employer’s ability to make changes depends on a number of factors. The starting point is what the change is and what the contract says - after all, this is the agreement that was reached between employer and employee. For example, a “mobility clause” is common in contracts of employment. A mobility clause allows the employer to require that the employee transfer either temporarily or permanently to another location, usually another place of business for the employer.
Where there are flexibility clauses in the contract and the employer tries to use them to make a change, the courts and tribunals often interpret them narrowly. That means that unless the change is clearly or specifically within the power of the clause then it is likely that the clause will not be a good basis for the change. The employer must also actin a fair and reasonable way so that what is called the implied term as to trust and confidence is not broken.
By way of examples, it has been found that changing shift patterns resulting in employees working increased hours was not permissible. An attempt to spread a teacher’s hours over five days instead of three days was not allowed even though the contract provided that the teacher’s hours were "subject to variation, depending upon the requirements of the school timetable".
Whether an employer can make the change proposed depends on the facts of the case. It is not an area where hard and fast rules can be drawn. If you, as an employer, are proposing to make changes or,as an employee, your employer, is proposing to make changes then legal advice is highly recommended.