Bombardier says Alstom, its supplier, hasn't been able to deliver a key software component.
Marc-André Lefebvre, a spokesman for the company, said 40 cars have already been completed.
One train is undergoing testing at night on the track in Montreal, and a second is being tested in La Pocatière.
However, Lefebvre said until the software can be installed, no more work can be done.
"It's the automatic train control software that operates some of the key elements of the train, and that element is necessary to continue testing," Lefebvre said. "If we don't continue testing, then we can't go into production of the vehicle itself."
Six month layoff
Lefebvre says the employees will be laid off from April until the end of October.
The Montreal transit agency, the Société de transport de Montréal (STM), ordered the new cars for its orange line at the end of 2010, and there have already been two major delays.
Lefebvre says Bombardier still expects to deliver the first trains on time, at the end of this year, and to complete the entire order by the end of 2018, as scheduled.
The STM expects to replace its 336 MR63 cars with 468 AZUR cars by 2018. The replacements were scheduled to begin in 2015.
Its MR73 cars, which first started running during the 1976 Olympics, will remain on the tracks until 2036. These cars will be moved to the green line.
Some 220 workers will remain on the assembly line in La Pocatière, fulfilling other contracts for subway cars for Toronto, New York City and San Francisco.