NYPD Interim Commissioner Thomas Donlon laid down the law in his first hours on the job, warning brass, “There’s only one voice in this department, and that’s me’’ — while privately describing the largest police force in the nation as in disarray, sources say.

But the temporary top cop’s strict “I’m the boss’ approach has its limits.

Mayor Eric Adams shot down Donlon’s first-week move to try to shake up the NYPD’s upper ranks by giving some higher-ups the boot, a law-enforcement source told The Post.

Insiders familiar with Adams’ thinking said the mayor doesn’t want to clean house without knowing the full scope of a federal probe that toppled former Commissioner Edward Caban.

Regardless, Adams still hopes Donlon, a retired FBI official with an impressive resume, will help rebuild the NYPD’s image until a long-term commissioner is appointed, sources said.

Sources insisted that Donlon feels secure in his position — even after facing a federal raid of his own over the weekend in a search for 20-year-old “materials” from a past job.

The new, if short-term, police commissioner flexed his muscles during his first sit-down with executive staff Sept. 13, sources said.

Donlon told those gathered in the executive command center that he planned to institute a “one voice” policy for NYPD messaging — a move that would effectively muzzle tweet-happy brass such as Chief of Patrol John Chell and Deputy Commissioner of Operations Kaz Daughtry on social media, insiders said.

The move rankled many brass, who view social media as key to their public-safety strategy, sources said.

But critics have long decried the aggressive recent social media posts by top officials as unprofessional at best.

NYPD officials have been quiet on social media since Donlon’s directive.

Photos tweeted from the meeting with Donlon show many sour-faced NYPD executives.

Sources said police brass were also taken aback by Donlon’s previously disclosed plan to effectively pause proactive police work, especially with the Community Response Team — a revamped version of the department’s disbanded anti-crime unit.

Donlon is also surrounding himself with a cadre of close advisers, sources said.

But any hopes Donlon has to jettison existing police brass will have to wait.

Insiders said Adams and City Hall officials view any NYPD shakeups as risky, given the federal investigation. Police officials are also reluctant to launch their own probe into potential wrongdoing out of fear it could step on the feds’ toes, sources said.

The prevailing view is that until the accusations being investigated by the feds are known, it’ll be foolish to move around police executives who may nor may not be involved, sources said.

Adams also wants to give the next permanent commissioner the chance to put who they want in the top departmental roles, according to sources.

Until then, Donlon is in charge — and his first department-wide message Monday emphasized collaboration.

“Together, we will make the safest big city in America even safer,” he wrote.

-Additional reporting by Joe Marino