CHICAGO (CBS) — The nation’s major freight railroads are threatening partial or total shutdowns Jan. 1, unless Congress extends the deadline for installing new signaling systems and software — and Metra and Amtrak are caught in the middle.

Metra said Thursday that it, too, would be forced to halt operations when 2016 dawns, in a letter to U.S. Sen. John Thune (R-South Dakota), the chair of the Senate Commerce, Science and Transportation Committee.

Metra CEO Don Orseno wrote Thune on the heels of letters from the chief executives of Union Pacific Corp., BNSF Ry., Norfolk Southern Corp. and CSX Transportation, all of which said they would halt some or all freight and passenger service unless Congress votes to extend the Dec. 31 deadline to install Positive Train Control (PTC) systems on all lines.

The threatened stoppage would halt the movement of everything from crude oil to perishable foods by the freight railroads. Orseno echoed the freight railroads, writing that Metra’s legal authority to operate would be in question.

“In the absence of an extension, there is a strong possibility that Metra will not be able to operate our trains beginning Jan. 1, 2016,” Orseno wrote. “Additionally, the two railroads with which we have purchase of service agreements — UP and BNSF — have stated that they do not plan to operate passenger rail until PTC is fully implemented and operational.”

The PTC system utilizes computes, radios and GPS to automatically slow or stop a train before it can become involved in a collision or derailment, even if the engineer falls asleep at the throttle or is disabled.

Orseno and the freight railroad chief executives wrote that installations are progressing, but are unlikely to be completed before 2018. Metra and the freight railroads have lobbied Congress for more than two years to extend the deadline.

He wrote that the fines alone would deal Metra a crippling blow. The Federal Railroad Administration (FRA) has said it will fine the railroads up to $25,000 per train if they operate without PTC.

“If these fines were to be paid by Metra, we anticipate they could cost our agency nearly $19 million per day,” he wrote.

Metra alone is spending $350 million on PTC installation.

The shutdown would not affect CTA rapid transit lines, which have employed a similar signaling system that is track circuit-based, unlike PTC, which relies on GPS. Orseno wrote that it has reached out to CTA and Pace to determine what could be done to carry some of its riders.

Metra operate 750 trains and carries an average of 300,000 riders each weekday. The BNSF and UP-operated lines alone carry more than 50 percent of those riders.

Although Amtrak said it has not been notified of any service suspensions because of the PTC deadline, the freight railroads said that is their intention. UP President/CEO Lance Fritz wrote that it would stop originating long-distance passenger trains “several days earlier to ensure that all passengers reach their destinations before the deadline.”

CSX has threatened suspension. Norfolk Southern and BNSF said their ability to operate Amtrak trains would be “uncertain.”