New York CNN Business  — 

The threat of a freight railroad strike has been pushed back to early December, as four major unions have agreed to coordinate the date on which they could potentially go on strike.

The third-largest railroad union, the Brotherhood of Maintenance of Way Employe Division, had been prepared to strike as soon as November 20, the Sunday before Thanksgiving. But the group announced Wednesday that is has agreed to extend negotiations with the railroads until at least December 4, the deadline set by another union, the Brotherhood of Railroad Signalmen. The rank and file members of both unions have rejected the tentative agreements reached with the railroads in September, mostly over the lack of sick pay in the contracts.

A strike by any one rail union would lead to a shutdown of America’s major freight railroads, as all the other unions, even those that have ratified contracts, would honor the picket lines. That could cause severe economic problems, as 30% of America’s freight moves by rail, when measured by weight and distance traveled.

The two largest rail unions, the Brotherhood of Locomotive Engineers and Trainmen and the Sheet Metal, Air, Rail and Transportation union, which represents conductors, are holding their own ratification votes, the results of which are due November 21. If one or both of those unions reject the deals, they would be prepared to strike December 9.

If one or both of those contracts are voted down, the BMWED said it is ready to further push its strike date back to December 9.

“If these unions do not ratify, then we will have the opportunity to bring all of rail labor together, under a single deadline, to finish national negotiations,” said the BMWED’s statement.

But reached Wednesday evening, Michael Baldwin, the president of the Signalmen’s union, said that he has not yet agreed to move his strike date back from the December 4 date.

The BMWED and Signalmen are engaged in negotiations with railroad management seeking deals that union leaders believe their members would ratify. The unions hope the extension will prevent Congress from imposing a contract or order them to keep working into the new year, when Republicans might be in control of one or both houses of Congress.

The unions want to maintain their ability to strike in order to increase their leverage with the railroads. Congress is due to return from recess next week.

Delaying the date of a threatened strike will “provide an opportunity to increasingly educate members of Congress — who have been out of session and consumed by the mid-term elections — about the railroad workers’ state of despair that management has created, and the railroad workers’ need for paid sick time off,” said the BMWED in a statement.

The unions are concerned that the November 20 strike threat would prompt the railroads to curtail services as soon as next week. The railroads did just that in the days before a marathon negotiating session averted a scheduled September 16 strike. The unions were also concerned that cutting service could prompt Congress, under pressure from freight rail customers, to rush through legislation to keep them on the job.

“With this extension, there is absolutely no reason for the railroads to discontinue services or threaten to discontinue their services,” the BMWED statement said. “There is now more than adequate time for the railroads to come to the bargaining table, engage in good-faith negotiations with us and reach a voluntary Agreement to provide all railroad workers with paid sick leave.”

But so far railroad management has rejected proposals by the rail unions for paid sick time out of hand.

The National Carriers’ Conference Committee, which negotiates with the unions on behalf of the major freight railroads, said it will “remain engaged with BMWED throughout the extended cooling off period.” But added that it will seek an agreement based on the framework of deals already ratified by the other unions.