Credit inquiries are permissible under FCRA 604 for non-credit business transactions, provided the transaction has an associated legitimate business purpose for the business to review your credit history as a part of the transaction.
Usual examples are cable and phone services, apartment rentals, and other transactions where there is a reasonable liklihood that you could end up owing the business for goods or services.
The issue is thus whether or not your transaction had a legitimate business need for them to review your credit.
Do you, in the course of your services, ever have goods or other services extended to you for which you may owe them?
As an aside, this sounds more like an employment credit check than a business transaction with them.
FCRA 604 requires that an employer must first request your permission, and then obtain express written consent prior to having permissible purpose to obtain your credit report for employment purposes.
Are they legally considered to be your employer?
If so, then you might have basis for a dispute of clear lack of permissible purpose if you did not give your prior written consent to their inquiry.
