Many members of the New York Police Department are furious at Mayor Bill de Blasio and, by extension, the city that elected him. They have expressed this anger with a solidarity tantrum, repeatedly turning their backs to show their collective contempt. But now they seem to have taken their bitterness to a new and dangerous level — by walking off the job.

The New York Post on Tuesday reported, and city officials confirmed, that officers are essentially abandoning enforcement of low-level offenses. According to data The Post cited for the week starting Dec. 22 — two days after two officers were shot and killed on a Brooklyn street — traffic citations had fallen by 94 percent over the same period last year, summonses for offenses like public drinking and urination were down 94 percent, parking violations were down 92 percent, and drug arrests by the Organized Crime Control Bureau were down 84 percent.

The data cover only a week, and the reasons for the plunge are not entirely clear. But it is so steep and sudden as to suggest a dangerous, deplorable escalation of the police confrontation with the de Blasio administration. Even considering the heightened tensions surrounding the officers’ deaths and pending labor negotiations — the Patrolmen’s Benevolent Association has no contract, and its leader, Patrick Lynch, has been the most strident in attacking Mr. de Blasio, calling him a bloody accomplice to the officers’ murder — this action is repugnant and inexcusable. It amounts to a public act of extortion by the police.

And for what?

Let’s review the actions that Mr. de Blasio’s harshest critics say have driven the police to such extremes.