Legal/ethical question about paternity testing

I work in a lab that has just begun to do parentage testing. Participants have two options: they can go the more expensive route which will stand up in court, or the less expensive route for the merely curious. (The difference is in the paperwork; the method is the same.)
We had a call yesterday from a lawyer’s office about a father who wants his two preteens tested to find out if they are his. He divorced the mother several years ago and has visitation and pays alimony, but he is not the custodial parent. His intent was just to find out if he is the father, he was not going the legally admissible route. We declined to do the test because he doesn’t have custody.
I was told by the lady from the lawyer’s office and by one of our doctors that other labs don’t have this requirement. In their view, they are providing a service and it’s not up to them to approve who’s buying. (The lady also told me that the father would still be responsible for child support no matter how things turned out.)
I can see both sides of this issue; after all, you can’t take my child off and get him a flu shot without my permission. On the other hand, this changes no one’s situation in a legal sense. Shouldn’t “Dad” be allowed to have his question answered?

Anyway, for the record, I think it’s a bad idea and I hope Dad changes his mind. But I’m still of two minds about whether our lab should require custody or the permission of the custodial parent. What do y’all think?