Liberal former late-night host Stephen Colbert had to be rushed out of an event at Harvard after someone pulled a fire alarm as hundreds of union protesters shouted outside over his decision to cross their picket line and give a talk at the school, according to reports.

Cellist Yo-Yo Ma took the stage with Colbert Thursday despite pleas from the Harvard Graduate Student Union urging them to cancel in solidarity.

Despite the protests, the union members denied responsibility for pulling the alarm.

“The alarm was unrelated to HGSU’s picketing activity and we have no knowledge of its cause,” wrote HGSU in a statement on social media.

“Members at the picket were relieved to learn that no one inside was at risk,” the statement continued.

The union was hoping that Colbert — who stood with protesters during the Writers Guild strike in 2023 and co-founded Strike Force Five — and Yo Yo Ma, a Harvard graduate, would avoid walking the picket line.

Even before the alarm, the celebrity appearance was disrupted by the union members chanting and demonstrating directly outside the venue, making it difficult to hear the speakers.

The fire alarm forced organizers to pull the plug during the question and answer portion of the talk and escort Colbert out of the venue.

HGSU has been on strike since Oct. 27, demanding a fair contract that includes wage increases and protections for non-citizens and harassment and discrimination.

Since the strike began, graduate classes have been untaught. 

The union said Colbert got plenty of warning that they would consider his appearnce to be crossing their picket lines.

“HGSU-UAW sent multiple formal communications to Colbert and Ma’s teams well in advance of the event that due to ongoing strike action, the building their event would be held at would be one with an active picket and that we encouraged them to move their event to an off-site location or virtually, reschedule the event, or cancel so as to not cross the picket,” wrote the union on Instagram.

“Colbert and Ma’s respective unions, SAG-AFTRA and the Boston Musicians’ Association, also reached out to them on our behalf with the same request,” the statement continued.

“They continued the event inside without regard for the picket line, and refused to speak with union members as they left the event. In other words — they crossed our picket line.”

John Green, an American author and YouTuber, stood in solidarity with HGSU and changed his schedule to accommodate the strike.

“They’re on strike and I had to move a thing to not cross a picket line,” he said in an interview clip posted to HGSU’s Instagram. 

“Which was an easy decision… it was not a hard decision for me. I’m sorry I had to do it on Zoom,” he continued.

“But I’m also sorry that the student workers have to be on strike against the richest university in the world.”

He donated the proceeds he earned from the event to the union, according to The Boston Globe.

The Harvard Graduate Student Union and representatives for Yo Yo Ma and Stephen Colbert did not immediately respond to The Post’s request for comment.