(a) Except as otherwise authorized under § 13-201(b) of this subtitle, a unit may not execute or renew a contract for the employment of a contractual employee unless the Secretary issues to the unit a certification that:
(1) the employment of the contractual employee is for services that cannot be performed by assignment or hiring of any nontemporary employee;
(2) the rate of pay for the contractual employee is comparable to the rate paid to employees in positions that involve comparable duties, responsibilities, experience, and authority; and
(3) the services to be performed under the contract encompass functions that:
(i) are infrequent;
(ii) are needed for a limited time;
(iii) are unusual; or
(iv) need to be implemented quickly and for which there is no reasonable alternative.
(b) The Secretary may issue a certification for any effective period that does not exceed the period of the contract between the unit and the contractual employee.