Pauley went on a Twitter rant last Friday vowing to never return to "NCIS," saying she was terrified of Mark attacking her ... and accused him of an actual assault.

In a since-deleted tweet, Pauley wrote ... "You think I didn't expect blow back? You got me wrong. THIS happened To my crew member and I fought like hell to keep it from happening again! To protect my crew!"

Then came her allegation ... "And then I was physically assaulted for saying NO!? and I lost my job."

Quick backstory ... that was all a reference to Mark's dog biting a crew member on set back in 2016, which left the guy with 16 stitches.

Sources familiar with the situation tell TMZ ... Pauley is now claiming that Mark body checked her on set in 2017 in what she perceived as payback. We're told Pauley felt it was an attempt to intimidate her after the dog fiasco.

Our sources tell us Pauley strongly objected to the dog being on the set after the bite and lobbied CBS brass to make it happen. We're told CBS eventually caved, telling Mark the dog would have to stay in his trailer unless it was leashed.

After CBS's new rule, we're told Pauley felt Mark only trotted the dog out when she was around -- which made things tense -- and their relationship was never the same. They hardly filmed any scenes together after that.

As to Pauley's claim she "lost" her job, our sources tell us it's unclear what she means exactly. We've been assured Pauley quit "NCIS" on her own accord in 2018.