State of play: A no vote from either or both of these unions would raise the threat level of a strike, swinging the balance of power in labor's favor.

• But even if both groups vote to ratify the deal, this isn't over. Three other, smaller unions have already voted against the contract and are now back in negotiations.
• The deadline to come to terms was already moved from last weekend to Dec. 4. If one of the unions votes no on Monday, the deadline will move to Dec. 9.
• After these dates, a strike could happen at any moment — unless lawmakers step in to implement a cooling-off period or even force the workers to accept a deal.
• "Our expectation is that no matter what happens, Congress is still going to need to step in," said Scott Jensen, director of issue communications, at the American Chemistry Council. It's one of many trade groups sounding alarms about the possibility of a shutdown.

Between the lines: The contract was brokered by union leadership and they've had a tough time selling the deal to rank-and-file members, many of whom are incredibly angry about how they've been treated in recent years — particularly during the pandemic.

• Union leaders trying to sell the deal to members have gotten a lot more blowback than they were expecting, in part due to a worker group — unaffiliated with these organized unions — that's been pushing hard against the deal.
• Unlike in a lot of labor deals, pay isn't the main sticking point. It's work-life benefits — particularly sick leave.
• "We were somewhat surprised," when members voted no, said Peter Kennedy, director of strategic coordination research at BMWED, the third-largest union, which voted down the contract in October.
• "This is the best pay package I've seen in my career," said Kennedy, a near-20-year rail veteran. "If employees are willing to vote that down because of the lack of paid sick time, that tells you something."