Fox News employees expressed outrage this week after Sean Hannity referred to his own network as "fake news" at a campaign rally with President Donald Trump.

CNN on Tuesday reported that more than a dozen Fox News staffers said they were disappointed by Hannity's decision to participate in a campaign rally in Missouri on Monday night.

"People throughout the company think a new line was crossed," one employee of the network told CNN.

"It disturbs me to my core," another Fox News staffer agreed. "I am so f---ing mad."

A third employee explained that staffers had been told that Hannity would limit his participation to interviewing the president.

"We were all told that Hannity was going to interview the president, but no one that I spoke with expected what happened last night," the employee said. "I'm aghast as are a number of other people."

Although Hannity promised in a tweet not to campaign with the president, he appeared on stage with Trump at the rally.

And to add insult to injury, Hannity referred to media in the room -- including Fox News employees -- as "fake news."

"By the way," Hannity told the crowd, "all those people in the back are fake news."