Workers take to picket lines after being locked out of BP refinery in Whiting, Indiana

Hundreds of workers were locked out of the BP refinery in Whiting, Indiana, on Thursday after contract negotiations failed to produce a deal ahead of a midnight deadline.

Since midnight Wednesday night, workers have been at the picket lines. They said they are willing to stay out as long as it takes.

The lockout took effect at 11:59 p.m. Wednesday, and affects more than 800 workers. Overnight, workers lined entrances to the refinery holding signs, honking horns, and settling in for around-the-clock picketing.

Union leaders say negotiations have stalled for months. They are accusing BP of rejecting their proposals on jobs, pay, and safety.

"Fighting for a fair contract, safety in the refinery, so we can all come home the same exact way we walked into the refinery," said employee Kelsey Nelson.

Union president Eric Schultz told CBS News Chicago that BP is demanding they cut 100 jobs and accept pay cuts to nearly all positions, something they won't accept. 

"The company has really refused to move much at all on their massive proposals, refused to acknowledge our proposals," Schultz said.

BP said it has made a comprehensive offer, and plans to continue operating the refinery with trained staff, adding that it does not expect disruptions to production.

Union members said they are prepared to stay out on the picket lines 24/7 until there is movement at the bargaining table.

More union representatives were expected to speak later Thursday morning, and CBS News Chicago is continuing to reach out to BP for an interview.

The Whiting refinery is BP's largest refinery in the world, producing 440,000 barrels a day. It is located less than 20 miles from downtown Chicago.