Can't see your are going to win this one Jimmy, client would only ask for cuts for two reasons -
1. Client is struggling themselves financially.
2. Your staff are doing a really good job, and the client believes that this gives them a good opportunity to cut their own costs.
I do not think that your client would yank your chain on this!
Regarding redundancies, I think that you will find that this is your responsibility, after all, they are employed by you, not your client.
If this was happening to me, I think that I would ask the client to work with me in implementing these cuts, you of course know that the building will not be able to be cleaned to the present standards with less hours spent on the job, so you should explain this to your client.
If your client knows and accepts this, try to work out the minimunm acceptable level of cleanliness with your client, you could for example do a full clean 3 times per week, and just bins and walkway for the other two days, or other permutations such as polishing/dusting every other day etc.
Yes your staff are not going to be happy, but then again that is your problem, not your client's, just be honest and straight with them, hopefully they will realise that you have very limited choices in this matter, after a while, perhaps your client will realise that the "New Way Of Doing Things" does not work, and they will go back to the original contract hours, which I assume that they have been happy with, not many clients understand the cleaning needs of their own buildings, and because of this, the cleaning is one of the first things to get cut when budgets are stretched, just look at what happens in hospitals.
You cannot ignore your clients request, after all, they are the ones in charge, however you should also check out the legal position of your contract with your client, as they surely must give you some notice before they change the contract in such a radical manner, however if you can work with your client, remain objective and act in a professional manner, you could do yourself a huge favour in the future, as the client will remember that you tried to understand their needs and behaved in a professional way, whilst still trying to get the job done.
best of luck on this mate.