PITTSBURGH — The city’s uniformed police officers have been given more time to comply with new rules that they wear bulletproof vests under their shirts and not wear baseball-style caps, even as their union filed a grievance to prevent the changes.

Stephen Bucar, a former FBI supervisor hired as the city’s public safety director in June, agreed to delay the new rules until Sept. 10, according to a memo obtained by a Pittsburgh newspaper. The rules were to have taken effect Monday, but are being delayed, in part, because the more formal uniform hats Bucar wants officers to wear weren’t available in time.

Meanwhile, the Fraternal Order of Police filed a grievance, saying officers have developed rashes or have found wearing the vests under their shirts were too hot or restrictive. The union also argues the more formal hats are “cumbersome,” another Pittsburgh newspaper reported.

Bucar met with the union last week and believes the vests make police look too “military” and that ball caps make them look like “mall guards,” according to the grievance.

Public safety spokesman Sonya Toler said research, including studies done by the FBI and U.S. Department of Justice, shows “that even slight alternations to the style of the uniform will change how citizens, including criminals, perceive the officer.”

Toler said Bucar wants uniforms to project an image of “power” and “authority.”

“However, he wants that message to be conveyed in a professional manner, not a tactical manner,” Toler said. “Wearing the vests on the outside conveys a tactical message that (Bucar) believes is not necessary during normal patrolling.”