Judge Richard Leon is giving the federal antitrust cops a nasty headache over the CVS-Aetna deal.

His recent decision to delay the merger through next summer — which squares with an exclusive Post report, citing insiders — reveals he is being “vindictive” while “acting as an imperialist district court judge,” according to a source familiar with the thinking within the Justice Department.

On Friday, Leon got CVS Health to agree to keep part of its business separate from Aetna, though it closed its $69 billion deal to buy the company in November.

Leon is being seen by experts and the Justice Department as taking very unusual steps in his handling of what is almost always a routine review of an antitrust settlement.

On Nov. 29, Leon presided over what was to be a normal hearing that included CVS agreeing to sell Aetna’s Medicare Part D business to WellCare Health Plans as a merger condition.

For his part, Leon said he was not going to be a “rubber stamp” and hinted strongly that the American Medical Association should submit a comment opposing the deal.

“I think it’s very unusual to ask for comments,” a former high-ranking Justice Department official not involved in the CVS merger said, adding that anyone can send comments for 60 days after settlement approval, but deals always close beforehand, and few submit them, thinking it is a pointless exercise. The department got an abnormally high 95 comments about CVS.

Leon reportedly got a little hot under the collar with the feds’ appeal of his decision against them when he in June approved AT&T’s $85 billion purchase of Time Warner. That appeal is still being heard.

“He has taken an adversarial posture with the Justice Department,” Wharton professor Herbert Hovenkamp, who is considered the dean of antitrust law, told The Post.

At the close of a CVS hearing last Tuesday, Leon and Department of Justice lawyer Jay Owen shared this exchange:

“Mr. Owen, one last thing.”

“Yes, your honor.”

“I was quite struck by your pleading in this case. It struck me as being tone-deaf. It was intemperate, and it was not helpful to the Court. It struck me as being unnecessarily defensive, if not hostile, to the role of the federal courts,” the transcript says.

“It’s not very common for a judge to call the DOJ hostile to the federal courts,” Hovenkamp said.

A Justice Department spokesman said, “We continue to respect Judge Leon’s role in these proceedings.”

Leon did not return calls.