Reviewing your credit report is just another way for an employer to try to gain insight into the type of person you are. Some employers will view late payments or unpaid bills as a reflection on the responsibility and judgment of the applicant.
Employers are held to specific guidelines about running your credit as mandated in the Fair Credit Reporting Act. For example, you have to consent to a credit check and the employer must warn you in advance if the results could impact their hiring decision. Several states have passed laws prohibiting employers from running credit checks and several more are considering similar legislation.