Hours after two NYPD officers were shot dead in their patrol car on Saturday, a memo attributed to the city's largest police union urged its 23,000 active members to not write any summonses or make any arrests unless "absolutely necessary." "We have, for the first time in a number of years, become a 'wartime' police department," the memo stated. The Patrolmen's Benevolent Association disavowed the memo, but their members turned their backs to the mayor at the hospital. Their stridency fits a pattern: for decades, police unions have done seemingly outrageous things to gain leverage for their members.

After an officer was indicted for shooting and killing 66-year-old Eleanor Bumpers in 1984, the Times reported that the PBA "suggested that officers in all the city's boroughs refrain from any action until directed to do so by a higher-ranking supervisor and that in the Bronx and Brooklyn, officers should also await instructions from a prosecutor." Hundreds of officers sought transfers as a show of solidarity, and to snarl the NYPD's administration. (A bomb later went off in the PBA's offices. No one was injured. The indictment against the officer was later dismissed.)

In 1986, when 11 NYPD officers were arrested for running a drug ring out of Brooklyn's 77th Precinct, the PBA instigated another slowdown in protest.

In 1992, 10,000 police officers descended on City Hall to protest Mayor David Dinkins's creation of the CCRB. Mayoral candidate Rudy Giuliani egged them on, and thousands stormed the Brooklyn Bridge, blocking traffic for 20 minutes. From the Times' report:

While the rowdier demonstrators refused to leave the City Hall area, most of the group crowded onto Murray Street between Church Street and Broadway, where they listened to sharply worded speeches from Mr. Caruso, Mr. Giuliani and, finally, Michael O'Keefe, the officer who was cleared by a grand jury recently in the shooting death of a Dominican man in Washington Heights. Many officers flooded the bars along Murray Street and drank openly on the street during the speeches.

During most of that time, there were no uniformed officers on the bridge, though four officers on scooters arrived shortly after noon. They did virtually nothing to control the crowd. At one point, a New York Times photographer who was taking pictures was surrounded by demonstrators, punched in the back and shoved. A police lieutenant told the photographer, Keith Meyers, that he should leave the bridge. "I can't protect you up here," the officer said. A New York Times reporter, Alan Finder, was also kicked in the stomach.

In 1994, then-Commissioner Bill Bratton assailed the PBA's role in successfully lobbying for a bill that would remove his ability to fire an officer for misconduct. (The governor would later veto the bill.) From the Times' report:

"The legislation would seriously reduce my ability to keep police in line," said William J. Bratton, the Police Commissioner. "It is perverse, done in the middle of the night. For the Legislature and the union, it is payback time."

United States Representative Major Owens, whose Congressional district in Brooklyn has endured major corruption scandals in three of its police precincts over the last decade, said he is considering subpoenaing leaders of the P.B.A. to testify before his subcommittee's hearings on discrimination in law enforcement.

"The P.B.A. is a monster that makes real reform impossible," Mr. Owens said. "It spends money in all sorts of ways that it is not accountable for. Its leadership doesn't even make an effort to be representative of the entire force. It has people in Albany."

In 1997, to protest Mayor Giuliani's insistence on incremental pay raises, thousands of officers took to the streets to block traffic, chanting "Rudy's a liar, set him on fire."

A month after those protests, a flyer surfaced in the police community that asked Mayor Giuliani and the Police Commissioner ''be denied attendance of any memorial service in my honor as their attendance would only bring disgrace to my memory.''

Ten years ago, Patrick Lynch and the PBA picketed outside Mayor Bloomberg's house to demand higher pay.

In 2011, PBA members stood outside a Bronx courthouse to protest the charges against the officers who were indicted in the ticket-fixing scheme; some of the protesters chanted "EBT!" at people standing outside a welfare office across the street.

This morning, after noting his displeasure with the officers who turned their back on the mayor, Commissioner Bratton told Matt Lauer that labor negotiations were one of the "moving currents" that contributed to the animosity between the Mayor's Office and rank and file police officers.

"There's a lot going on in the NYPD at the moment—labor negotiations. Some 10,000 of our officers are in a new pension system that significantly limits their benefits," he said. "This occurred about four years ago when Governor Paterson signed a bill at midnight, there's a lot of anger about that because we've had so many attacks on young police officers over the past year."

On WNYC, Governor Cuomo declined to criticize Lynch for his comments directly blaming Mayor de Blasio for the murder of Officers Wenjian Liu and Rafael Ramos.

"The mayor has my full support, the union leaders have my full support, the community activists have my full support," Cuomo said. "Lets bring the temperature down and the rhetoric down and the dialogue down."

While Mayor de Blasio just announced an agreement with eight of the city's labor unions, the PBA and the Sergeants Benevolent Association are choosing to go into binding arbitration.

Representatives at the PBA have not responded to a request for comment.

Eugene O'Donnell, a professor at John Jay College of Criminal Justice and former NYPD officer, said that while the PBA is being demonized, the "real issue" is lack of accountability among politicians, who make the laws that the police enforce.

"'I'm an Assemblyman, I'm a Senator, I'm an architect of this system, I'm an owner-operator, the cops are our partners.' I haven't heard anybody say that," O'Donnell said.

"People want to focus on Lynch's particular language. Lynch was standing in an emergency room where two of his members were assassinated. I don't think he had a lot of time to come up with better language than he used." He added, "That's what the PBA does. They represent their members, who have a unique job, and who apparently in this environment have become orphaned."

O'Donnell says that since the Wilson and Garner decisions, beat cops have been scapegoats for those with real power.

"People will not explain what the police do, the context in which they operate, the power they have, the endorsement they have from the highest level of people. The root of this, is that loose cigarette enforcement is a lunatic mission, that no cop ever joined the NYPD to be part of."