Amazon confirmed to Fortune the origins of the fire and that “a handful of employees have been placed on investigatory suspension” while the company investigates the events. 

Amazon union leaders told the Post that workers had a hard time breathing amid the smoke. They added that one worker ended up in the hospital, but the Amazon said they received no such reports.

The fire occurred before a shift changeover: While day shift workers were sent home with pay, night shift workers claimed to CBS New York they weren’t warned of the fire before coming into the warehouse, where they say smoke still lingered.  

“They didn’t show us proof it was safe to work there,” warehouse employee Eli Andino told the local outlet. “They just told us just to work right through it.”

“It’s just point-blank an unsafe work environment,” added his coworker Leo Shockey. 

In response, about 100 workers protested by refusing to work under said conditions. A video posted by Amazon Labor Union shows workers chanting “Send us home.”

“The workers didn’t feel safe going back to work. They were engaging in rights that have been protected for 85 years under the National Labor Relations Act,” Seth Goldstein, labor attorney for Amazon Labor Union, told the Post. He added that the resulting suspension, which reportedly included a dozen union leaders and 40 warehouse workers, was a “violation of workers’ rights.”

Paul Flaningan, an Amazon spokesperson, tells Fortune that workers present at the time of the fire were safely evacuated and that the warehouse was deemed safe for the next shift of workers.

“The FDNY certified the building is safe, and at that point, we asked all night shift employees to report to their regularly scheduled shift,” he says. “While the vast majority of employees reported to their workstations, a small group refused to return to work and remained in the building without permission.”

The Amazon Labor Union says otherwise. “The ‘small group’ that refused to return to work was 30% of the building by management’s own admission, and many of those [who] did work simply didn’t know the spontaneous sit-in was in process,” they wrote on Twitter. “Many workers accidentally joined the action because they’d come by the office to complain.” 

They added to the Twitter thread that management is saying as many as 80 workers involved were suspended. 

Employees at the Staten Island facility long campaigned for union recognition, voting in a historic election to join the independent Amazon Labor Union this April. The results in the Staten Island facility represented a big win, as the collective became the first U.S. union at the company. 

Amazon has pushed back against the union and CEO Andrew Jassy has vocally questioned the veracity of the vote, citing what he deemed to be “a lot of very disturbing irregularities.” The fight for union recognition continues, as employees in Albany will vote this coming week on whether they’re joining the Amazon union.