The head of Amtrak has warned lawmakers that it will suspend service on parts of its national network by December unless Congress extends its deadline for implementing advanced safety technology, according to a letter obtained by Fox News.

The letter sent Monday by Amtrak Chairman Joseph Boardman to Senate Commerce Committee Chairman John Thune, R-S.D., outlined efforts to install Positive Train Control (PTC) to enhance train safety.

The Rail Safety Improvement Act, passed in 2008, set a Dec. 31, 2015, deadline for most commuter and freight trains to be overhauled with PTC -- a new GPS monitoring and safety network aimed at preventing deadly accidents like the recent Amtrak derailment in Philadelphia that left eight dead.

PTC regulates train speeds electronically by automatically slowing down trains as they head toward sharp turns or crowded area.

In the letter, Boardman said that Congress must act to extend the deadline to install the system as host railroads are not expected to meet the deadline.

“Should Congress fail to pass legislation to extend the PTC deadline beyond December 31, 2015, there will be significant impacts to our service and on our customers and tenant railroads,” Boardman said.

“The potential impacts would also be substantial, since a vast majority of our network would be inoperable without an extension of the deadline,” he said.

Boardman went on to say that Amtrak anticipates that, starting Dec. 1, the company would need to begin notifying passengers of disruptions due to the PTC deadline. Boardman also noted that the cuts would affect both passenger and freight services.

Passenger service would continue on track that Amtrak owns, including a large part of the Northeast Corridor between Washington and Boston. But service through parts of Connecticut and New York would be affected. 

The project timeline was adhered to in some cases. The system already is working in some states in the Northeast and in California.

Fox News' Chad Pergram and Matt Finn contributed to this report.