CNN said on Thursday that it would not run a new ad from President Donald Trump’s re-election campaign, saying that the 30-second spot about former Vice President Joe Biden contains inaccuracies and unfairly attacks the network’s employees.

The ad, released online last week, targets Biden and his son, Hunter Biden, amid a widening impeachment inquiry into Trump’s efforts to pressure Ukraine to investigate the Bidens. It repeats unsubstantiated allegations about the Bidens’ financial dealings in Ukraine and derides journalists as the Democrats’ “media lap dogs,” as footage plays of several CNN stars.

It is unusual but not unprecedented for television networks to reject a political advertisement from a presidential campaign. On the eve of last year’s midterm elections, major channels — including Fox News — removed an inflammatory commercial from Trump’s political team that portrayed immigrants as a violent threat.

The move by CNN is also likely to inflame longstanding tensions between the news network and the president, who denounced CNN staff members as “corrupt people” during a White House news conference Wednesday.

The Trump ad, titled “Biden Corruption,” was posted online Friday as part of what the president’s campaign said was a multimillion dollar advertising buy on national cable stations and digital platforms.

Over grainy footage of Joe Biden, a narrator intones that the Democratic front-runner “promised Ukraine $1 billion if they fired the prosecutor investigating his son’s company.” As video of House Speaker Nancy Pelosi plays, the narrator continues: “But when President Trump asks Ukraine to investigate corruption, the Democrats want to impeach him.”

The narrator adds, “and their media lap dogs fall in line,” over footage of CNN anchors Don Lemon and Chris Cuomo and the network’s chief White House correspondent, Jim Acosta. MSNBC host Rachel Maddow is featured as well.

No evidence has surfaced that Biden intentionally tried to help his son by pushing for the Ukrainian prosecutor general, Viktor Shokin, to be dismissed. Members of the Obama administration, as well as other Western governments and international leaders, had sought Shokin’s removal amid accusations that he ignored corruption claims. Shokin was voted out by the Ukrainian Parliament in 2016.

CNN said in a statement Thursday the ad failed to meet the network’s advertising standards. “In addition to disparaging CNN and its journalists, the ad makes assertions that have been proven demonstrably false by various news outlets, including CNN,” a network spokesman said.

Tim Murtaugh, the communications director for Trump’s reelection campaign, responded in a statement that the ad was “entirely accurate and was reviewed by counsel.”

“CNN spends all day protecting Joe Biden in their programming,” Murtaugh wrote. “So it’s not surprising that they’re shielding him from truthful advertising, too.”

CNN’s decision was first reported by The Daily Beast.

On Wednesday, Trump’s campaign introduced an additional 30-second ad related to the impeachment inquiry, which a narrator describes as “nothing short of a coup” that “must be stopped.”

Trump has said his request for help digging into the Bidens’ business deals was legitimate and part of a “perfect” phone call with President Volodymyr Zelenskiy of Ukraine. On Thursday, Trump publicly asked China to investigate the former vice president.

This article originally appeared in The New York Times.