New York (CNN) Fox News journalists were outraged and disgusted after Sean Hannity, the network's star host, campaigned with President Donald Trump on Monday night ahead of the midterm elections, more than half a dozen employees told CNN Business.

"People throughout the company think a new line was crossed," one senior Fox News employee told CNN Business on Tuesday.

"It disturbs me to my core," said another senior Fox News employee, who added, "I am so f---ing mad."

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

The Fox News employees all spoke on the condition of anonymity because they were not authorized to publicly discuss the matter.

Some of Fox News' biggest names, including Hannity, the hosts of " Fox & Friends ," and Jeanine Pirro — who also appeared with Trump on stage Monday night — have turned into full-time Trump supporters on television over the past two years. Some, like Hannity, Pirro and Fox Business Network host Lou Dobbs, reportedly even act as unofficial advisers to Trump at times. But Monday night's rally crossed a new line, making explicit what had long been implicit.

The Trump campaign had promoted Hannity over the weekend as a "special guest" at Trump's final rally before Tuesday's midterm election. But a Fox News spokesperson told CNN Business and other news outlets soon after that Hannity would simply be at the rally in Missouri to broadcast his show and cover the event for the network. Hannity offered an identical message in a Monday morning tweet, saying, "To be clear, I will not be on stage campaigning with the president."

Yet just hours later, Hannity and Pirro were both on stage with Trump, energizing the Republican base ahead of Election Day.

After having expressly denied that he would be campaigning on stage with the President, the first move from Hannity when he walked on stage was to slam members of the media stationed at the back of the auditorium as "fake news," apparently not realizing -- or caring -- that Fox News journalists were among the "people in the back" that he had insulted.

One Fox News employee described to CNN Business the scene at the New York headquarters of Fox News at the time, as a number of journalists inside the company's news division watched the episode unfold live. The person said that the employees were dismayed at what they saw.

Other Fox News employees questioned why network executives have not taken any action.

"The whole thing is just so embarrassing that this guy basically has free rein to do whatever he wants, and management is either helpless or uninterested in doing anything about it," said one Fox News employee.

Another employee said that Hannity's behavior, both Monday night and generally, "continues to make the task of the news side all that much harder."

One former senior Fox News employee told CNN Business that he had spoken to a number of former colleagues who are still at the network about the matter. He described them as "livid."

In a Tuesday afternoon statement, a Fox News spokesperson said, "Fox News does not condone any talent participating in campaign events. We have an extraordinary team of journalists helming our coverage tonight and we are extremely proud of their work. This was an unfortunate distraction and has been addressed."

Asked by CNN Business exactly how the matter had been addressed, the spokesperson declined to elaborate.

Hope Hicks, chief communications officer for Fox — the soon-to-be parent company of Fox News — did not respond to a Tuesday morning email asking whether Rupert or Lachlan Murdoch, the father and son who control Fox News, had any comment on or approved of Hannity's behavior.

Hannity, for his part, released a statement on Twitter saying, "What I said in my tweet yesterday was 100% truthful. When the POTUS invited me on stage to give a few remarks last night, I was surprised, yet honored by the president's request. This was NOT planned. And to be clear, I was not referring to my journalist colleagues at FOX News in those remarks. They do amazing work day in and day out in a fair and balanced way and it is an honor to work with such great professionals."

Hannity has for years flouted the usual standards required of Fox News employees. In 2016, for instance, he cited unscientific polls on-air after a Fox News executive told network producers that they did not meet the company's editorial standards.

But Monday night's appearance at Trump's rally was one of the clearest examples to date of Hannity's growing invincibility at the network.

While Hannity has been able to get away with breaking normal protocol, the network had previously attempted to rein him in.

When he appeared in a Trump 2016 campaign ad, a Fox News spokesperson said the network "had no knowledge" of Hannity's participation and said he would "not be doing anything along these lines for the remainder of the election."