New York Police Commissioner William Bratton is asking NYPD officers to show respect on Sunday when Mayor Bill de Blasio speaks at the funeral for slain NYPD officer Wenjian Liu, according to USA Today.

Officer Wenjian Liu, 32, and his partner, Officer Rafael Ramos, 40, were fatally shot on Dec. 20 while sitting in their patrol car in Brooklyn. The man charged with killing the officers, Ismaaiyl Brinsley, 28, then took off and shot himself in a nearby subway station.

According to the NYPD's Chief of Detectives Robert Boyce, Brinsley had posted anti-police and anti-government messages on his Instagram account in light of the deaths of Michael Brown and Eric Garner, two unarmed African-American men who were killed by police, before he attacked the cops.

The police unions blamed the New York City mayor for contributing to what they see as growing anti-police sentiment and being supportive of anti-police protests throughout the city.

Union leaders also took offense when the mayor admitted to forewarning his biracial son to take caution when interacting with police officers in wake of the death of Eric Garner.

In addition to being slammed by police unions, a number of NYPD cops turned their back on Mayor de Blasio at a police graduation ceremony at Madison Square Garden on Monday. Although most of the audience applauded for the embattled mayor, some members of the New York Police Department could be heard booing and heckling de Blasio. At one point, more than a dozen officers stood up and turned their backs against the mayor.

City cops also displayed this same pose of disrespect when the mayor spoke during Officer Rafael Ramos' funeral on Dec. 27, 2014.

In light of Officer Liu's funeral, Bratton warned officers not to use the service as an opportunity to express their dismay against the mayor.

In a memo to the officers, Bratton reminded them that they have a responsibility to their position, reports USA Today.

This act has become the focus of the "city's and country's consciousness," Bratton said.

"It stole the valor, honor and attention that rightfully belonged to the memory of Detective Rafael Ramos' life and sacrifice. That was not the intent, I know. But it was a result," he said.

"A hero's funeral is about grieving, not grievance."

Bratton also noted he has not made any mandates and will not discipline anyone who stands in defiance against the mayor.

"I issue no mandates, and I make no threats of discipline, but I remind you that when you don the uniform of this department, you are bound by the tradition, honor and decency that go with it," Bratton said, reports The Associated Press.

Related