Andrea Fox fought back tears as she described the meeting, saying former CFMEU state leader Michael Ravbar threatened to have her "physically dragged downstairs" and thrown into the street.
But Mr Ravbar has denied scaring Ms Fox, saying he was "blunt" but never raised his voice in an exchange he claimed lasted only a few minutes.
An emotional Ms Fox said a "menacing" Mr Ravbar blocked her only exit as he stood over her, saying she disgusted him and the union would not work with her.
She broke down on Tuesday as she told an inquiry into the Queensland CFMEU about what was meant to be a routine meeting at the rogue construction union's office in January 2018.
At the time, she was the state's director of work and electrical safety policy and had recently helped steer major workplace safety reforms through parliament.
Ms Fox - now Queensland's Office of Industrial Relations Policy and Workplace Services executive director - told the inquiry she had gone to the union office with two colleagues to meet with then-CFMEU president Royce Kupsch.
About 15 minutes into the meeting, Mr Ravbar appeared and took Mr Kupsch out of the room, she said.
Mr Kupsch returned and asked her to come with him, leaving her colleagues behind, Ms Fox said.
She arrived in another room and heard the door behind her "close and click" before turning around to see Mr Kupsch and Mr Ravbar standing between her and the exit, the inquiry heard.
Mr Ravbar - who Ms Fox had never met before - then went on an "angry tirade", she said.
He allegedly told her "people like you disgust me", declared the union refused to work with her and she was banned from entering any CFMEU building, site or meeting.
"He described how he would have liked to have me physically dragged downstairs and out of the building and thrown onto the street," Ms Fox said.
Her evidence comes as the inquiry examines claims the powerful construction union effectively "captured" Queensland's workplace watchdog and used its clout to pressure regulators behind closed doors.
"His voice started as a kind of hissing, low voice with gritted teeth and then got louder and more enraged as he went on," Ms Fox said of Mr Ravbar's "very menacing" tone.
"He was glaring at me and almost spitting at me … I felt in danger.
"He was full of rage and very unhinged ... I thought I needed to watch carefully for any sudden movement so I could be ready to duck as I was expecting that Mr Ravbar was about to physically assault me."
Ms Fox said she believed the confrontation was a "trap" designed to separate her from her colleagues so there would be no witnesses.
Mr Ravbar denies he threatened Ms Fox, saying he told her the CFMEU could no longer meet with her after feedback indicated she was impeding codes of practice amendments being sought by the union.
"I said words to the following effect ...'I'll be blunt. We are hearing you are the roadblock ... we think you are speaking with a forked tongue'," he said in a statutory declaration tendered to the inquiry.
"At no time did I yell or shout at her during the meeting. She was not locked in the room.
"At no time did I say she should be dragged out of the building. The entire exchange would not have lasted more than five minutes."
The inquiry, led by Commissioner Stuart Wood, has been extended by the state government until December and has heard months of evidence about the union's alleged influence over Queensland's construction industry and regulators.
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