Two of the largest railway unions were at odds when voting on a key labor pact this week, negating efforts from the White House to avoid a costly labor strike when the temporary agreement ends in December.

The clash doesn’t necessarily mean there will be a strike, but it does nudge union leaders to reach a better deal before the December 9 deadline. The ticking clock could also motivate Congress to step in to impose a labor agreement against unions’ will. Although politically unpopular for the Democrats, the ramifications of that move would still be less than the significant supply chain disruptions before Christmas.

Ag groups such as the National Grain and Feed Association are urging Congress to prevent a rail shutdown, which would only compound current transportation issues stemming from a dry Mississippi River.

Read more on the potential rail strike here.