Hello my name is XXXXX XXXXX I am happy to help you today. Have you been working the same overtime hours for a period of 3 years. Is it only you who is affected by this?
what reason have they given for this?
how many hours is it a week?
Are you paid an overtime rate/
Have you already raised an objection or is this your first point of call?
You have an argument that through custom and practice this overtime now forms part of your contract and it amounts to a breach of contract for these hours/ this pay to be taken away from you. If I were you I would submit a formal grievance about it before it gets to the interview stage.
If they insist that it is not contractual then you will have to object and consider bringing a claim in the employment tribunal on the basis of breach of cotnract.
If you have any further questions about this please do ask.
Hello please let me know if you need any further information and good luck with it.