"The PELRB's findings of fact are deemed prima facie lawful and reasonable, and its order prevails in the absence of a clear showing of unreasonableness or illegality." Appeal of Hinsdale Fed'n of Teachers, 138 N.H. 88, 90, 635 A.2d 480, 481 (1993); see RSA 541:13 (1997). As a preliminary matter, we review the applicable provisions of the CBA. Article 12 provides a procedure for off-duty officers to volunteer for extra details.

Appeal of Alton School Dist., 140 N.H. 303, 308, 666 A.2d 937, 940 (1995). The PELRB's factual findings are deemed prima facie lawful and reasonable. Appeal of Hinsdale Fed'n of Teachers, 138 N.H. 88, 90, 635 A.2d 480, 481 (1993). To succeed on appeal, the district must show that the PELRB erred as a matter of law or that its decision was unjust or unreasonable by a clear preponderance of the evidence.

Absent such a contractual provision, the PELRB has the "discretion to determine whether a dispute involves a matter covered by a collective bargaining agreement." Appeal of Hinsdale Fed'n of Teachers, 138 N.H. 88, 90, 635 A.2d 480, 481 (1993). The CBA defines a grievance as "an alleged violation of any of the provisions of this Agreement."