First off, this happens all the time in the US, which of course does not necessary make it correct.
I you hire someone to come in and clean, either an employee or a stranger, be careful that they are not acting as an employee under the IRS rules. The key test is not how you pay them, but rather the nature of the engagement.
If you provide the tools (mop, broom etc.), place where the work is done (your office), define the manner in which the work will be done, prescribe when it will be done, who will do it etc. you are defining a job that is dangerously close to being classified as an employee.
See the IRS page Independent Contractor (Self-Employed) or Employee?
Some key conditions which might make it OK include:
1) Your employee runs a cleaning business and has many other customers.
2) Your employee sends in someone other than themselves that work for the cleaning business to clean your office.
3) Your employee's cleaning business provides their own supplies and tools.
4) Your employee has all the proper business licenses and insurance.
5) Your employee files and pays all the appropriate taxes for their cleaning business.