Calcium build up in the trap will prevent the urinal from discharging as much water as the flush valve will allow. Or it could be that calcium and other minerals have reduced the actual diameter of the pipe. When this happens, water will back up because of the restricted flow.
Have licensed plumbing specialists scrape the pipe clean by using cutting blades. You can clean urinal traps by soaking them in vinegar over night. The vinegar will dissolve and remove the calcium and minerals.
As an ongoing preventative maintenance, you may want to purchase a drain care product that dissolves calcium. Also, Roto-Rooter Urinal Blocks deodorize and eliminate calcium build up inside drain lines. Each 4 once block lasts for approximately 500 flushes.
Roto-Rooter can assist in your commercial plumbing needs.