While President Trump’s Department of Justice sues to block AT&T’s acquisition of Time Warner, it’s also eyeing a clampdown on Comcast.

Federal law enforcement is weighing an extension of a six-year-old probationary period over Comcast’s merger with NBCUniversal, concerned that the Philadelphia-based cable giant has been playing fast and loose with competition rules, sources told The Post.

Under a 2011 “consent decree” it signed to get its NBCU merger cleared by the Justice Department, Comcast promised it wouldn’t withhold NBC programming from rival cable companies or over-the-top competitors — a truce designed to encourage competition in the cable TV industry.

The DOJ isn’t currently probing the matter, sources emphasized. But earlier this month, fresh accusations of bad behavior surfaced when smaller cable rival RCN accused Comcast of overcharging it for NBC broadcasts in a filing with the Federal Communications Commission.

The FCC isn’t expected to take action, but insiders say RCN is laying the groundwork for a federal complaint against Comcast before its consent decree expires next fall.

“I don’t think Comcast has heard the end of it” from the Justice Department, said Daphna Ziman, president of TV network Cinemoi.

Ziman, a longtime advocate for independent programmers, testified against the AT&T-Time Warner merger at a US Senate anti-trust subcommittee hearing. She says US officials have recently voiced lingering concerns about Comcast in private conversations.

“The DOJ feels like [the consent decree] was a big mistake” and now believes it should have sued to block Comcast’s NBCUniversal acquisition altogether, she said.

Some antitrust experts argue that if the feds stop AT&T — which owns pay TV giant DirecTV — from owning valuable content such as that of Time Warner’s HBO, it should at least keep a tight rein on Comcast so it can’t wrongfully exploit its ownership of NBC.

“There is no credible basis to pursue an extension or modification of the consent decree or conditions,” a Comcast spokeswoman said Tuesday. “For nearly seven years, Comcast has met or exceeded all of the commitments and obligations under the NBCUniversal transaction.”

Rival RCN begs to differ. In its FCC filing this month, RCN argued Comcast’s probationary period should be extended after it expires next month. The Justice Department consent decree expires Sept. 1.

An “unleashed Comcast-NBCU is certain to wreak havoc in the market, undermining rival distributors and harming consumers throughout the country,” RCN said.

Elsewhere, the FCC in 2012 investigated Comcast for not offering customers a reasonably priced broadband option if they didn’t want cable. The agency ended up extending its protective order governing the Comcast-NBCU merger by a year.

In 2013, the FCC sided with Bloomberg TV when it sued Comcast for exiling its channel to the far end of the menu. In Washington, DC, for example, CNBC was on Channel 39 next to Fox and CNN, while Bloomberg was on Channel 103, next to C-Span, according to Wired.

Meanwhile, news reports in 2013 alleged that Comcast — which as part of its DOJ consent decree was supposed to be only a passive investor in Hulu — stopped Hulu from selling itself to rival DirecTV by cutting a deal to invest more in the streaming service.

Despite those disputes, a source familiar with Comcast’s thinking said extending the NBC consent decree will not be easy.

“Yes, they can if they have evidence Comcast is not a good actor, but it is a very high burden” the DOJ will need to prove in court, the source said.

Comcast last week said it would give more than 100,000 workers a special $1,000 bonus to celebrate tax reform and the end of net neutrality.

The Justice Department declined to comment.