Sinclair Broadcast Group has agreed to air a commercial from a liberal consumer watchdog that's critical of the broadcaster's actions. But there's a catch.

The company is running its own message right before and after the ad. So viewers are seeing a 15-second defense of Sinclair, then 30 seconds of criticism, then another 15-second defense.

The unusual move comes one week after Sinclair was roundly criticized for requiring anchors at dozens of local stations to record a media-bashing promo. To many observers, it sounded like the anchors were echoing President Trump's talking points.

Sinclair defended the ad, but journalists at numerous stations expressed alarm about the corporate mandate.

The liberal consumer watchdog group Allied Progress seized on the controversy to mount a campaign against Sinclair's proposed acquisition of Tribune Media's TV stations. On Thursday the group announced what it called a "six-figure ad buy" to condemn Sinclair.

"Tell the FCC to stop the Sinclair merger," the ad said.

Related: Sinclair producer in Nebraska resigns to protest obvious bias

The group sought air time on four Sinclair-owned stations -- WJLA in DC, KDSM in Des Moines, KOMO in Seattle, and WBFF in Baltimore, right down the road from Sinclair headquarters. But there was ample skepticism about it. Would Sinclair actually accept the ads?

Sinclair did approve the ad buy and the ads started running on WJLA on Saturday with a disclaimer on both sides. A corporate spokeswoman declined to comment on the matter.

Allied Progress executive director Karl Frisch commented to CNN, "They defend forcing anchors to parrot the anti-media talking point and attack Allied Progress."

Here's how the Sinclair message starts:

"This station, which is owned by Sinclair Broadcast Group, is proud to present both sides of issues. For that reason, we have agreed to air the commercial you are about to see, opposing Sinclair's acquisition of additional television stations. We think the ad is misleading, but wanted to let you decide. Thank you."

Related: Sinclair responds to criticism of media-bashing promos

Then the Allied Progress ad begins:

"What happens when local news isn't local? This."

The ad shows Deadspin's viral video compilation of the promos assailing "fake" stories and "biased" journalists.

"Sinclair owns this station and nearly 200 others. It forced dozens of anchors to recite the same political message, word for word," the Allied Progress voiceover says."Now Sinclair is trying to control local news stations in 72% of American homes. Tell the FCC to stop the Sinclair merger."

The ad urges viewers of Sinclair stations to call the government regulator and oppose Sinclair -- an awfully unusual sight.

Related: Sinclair tells anchors to run media-bashing promos and the criticism goes viral

Sinclair may have calculated that refusing to run the ads would have simply drawn more attention to Allied Progress's campaign.

So instead this message pops up right afterward:

"The misleading ad you just saw focused on a brief promotional message that simply said we're a source for truthful news," the Sinclair voiceover says. "It ignored thousands of hours of local news we produce each year to keep you informed. The ad was purchased by a group known for its liberal bias, and we hope you won't buy into the hysteria and hype."

The remark that Allied Progress is "known for its liberal bias" is eyebrow-raising, since the group makes no secret of the fact that it supports liberal causes.

Much of the controversy -- what Sinclair calls "hysteria and hype" -- is about assertions that Sinclair presents a conservative bias in its local newscasts.