"We've been here since yesterday and last night, and we're not going anywhere. We are committed to this," worker Melvin Maclin said.
The protestors are calling their demonstration a peaceful occupation. Some 200 workers at Republic Windows and Doors are staying inside their plant, in shifts, even though the company has told them that - as of yesterday - their jobs no longer exist.
"I do whatever I have to do to support my family," said Armando Robles, who also was laid off.
Robles, a husband and father of three children, says Republic's abrupt closing means no more health insurance for his family. He and other members of the unionized, largely Hispanic workforce have been told that they should not expect any severance or vacation pay they say they've already earned.
"Chicago is a working class town. We're gonna stand together 'til we win this battle," one union leader said.
Saturday afternoon, members of other unions rallied in support of the Republic workers. Their argument is that the company violated federal labor laws by not notifying the workforce at least two months in advance of its plan to close.
Employees say they got the news only four days ago. Illinois law requires a 75-day notification if a company the size of Republic intends to close its doors.
"And what that does is, it allows workers to go into the collective bargaining agreement, to renegotiate terms of the contract to make sure they get everything that's entitled to them," DePaul Univ. Labor Educator Cynthia Martinez.
Republic has reportedly suffered a huge, rapid decline in sales, and the company maintains it had no choice but to shut down.
"It's clear to us that the company has been moving resources and production elsewhere," said Rep. Luis Gutierrez of Chicago.
Congressman Luis Gutierrez also says he's seeking answers at a meeting with Republic and its lender, Bank of America, Monday afternoon.
Meanwhile, the workers say they're staying at the building.
"I'm gonna stay to the end. If they're gonna tell me I have to leave, they have to arrest me. I'll take the chance," one worker said. "I'm prepared to be arrested if necessary," Armando Robles said.