In grievances over disciplinary actions, the agency has the burden of establishing by a preponderance of the evidence that the disciplinary action was justified, provided, however, that in a grievance concerning suspension without pay pursuant to section 610(a)(3) of the Act, the Board's determination of the grievance shall be limited to:

(a) Whether the required procedures have been followed; and

(b) Whether there exists reasonable cause to believe a crime has been committed for which a sentence of imprisonment may be imposed and there is a nexus between the conduct and the efficiency of the Service.

For this purpose, reasonable cause to believe that a member has committed a crime for which a sentence of imprisonment may be imposed shall be defined as a member of the Service having been convicted of, and sentence of imprisonment having been imposed for, a job-related crime.