My daughter and I discussed this in the van on the way to the Pennsylvania Catholic Homeschooling meeting this morning.
What we decided was that if the people doing the job are not exposed to immoral actions or situations (such as being outside of the house and the people that live there not being sexual toward one another gay, heterosexual or other) then the anti-discrimination laws would prevail. On the other hand if you were asked to do the landscaping or yard work at a business that promotes an immoral life style you should have the privilege of saying no thank you for the job.
But if it was cleaning inside of a home or office then you have other considerations. Do you clean up after them physically? Are you exposed to their lifestyle with items eg. pictures and personal items? Do they act out in front of you? Then it should be up to you if you provide the service to them or not. This includes all situations single, married, gay, divorced etc. It is my decision to go into a home or not.
I would never clean up an office or home were I was exposed to occult items, sexual innuendo or other morally offensive (to me personally) situations.