Depending on what your contract says, your company may be able to reduce your working hours in this manner, dependent on the needs of the business, but I believe they can only do this for a total of 4 weeks. Any longer and it then needs to be a change to your contract in which case I believe that they must give you a months written notice of the change. From what I understand you then have the chance to agree or refuse the new contract. If you refuse though and cannot agree new terms with your company, you stand the risk of being out of a job. This is a very simplistic explanation and I am sure someone like Ethel or Builders Mate will be able to give you more professional advice, but at least I have given you somewhere to start from! Best of luck, I would ensure that you get further advice if this starts to drag on too much.
Cheers Sue