OC Transpo's largest union is "very disappointed" after the transit service revealed it is looking to cut between 500 and 600 positions once LRT comes online in 2018.

"I've been blindsided, absolutely, by the numbers," said Clint Crabtree, president of Amalgamated Transit Union Local 279. "I didn't have anything in mind or have any ideas of the numbers — not at this point — but when I was presented the numbers, I was very disappointed."

Transit boss John Manconi wrote in a memo to council that he met with three union leaders, including Crabtree, on Monday to discuss the cuts and ask for ideas to minimize layoffs.

I've been blindsided, absolutely, by the numbers. - Clint Crabtree, ATU Local 279

The city estimates that light rail will take 170 to 180 buses off the road. One light rail train carries the same number of passengers as eight articulated buses. That means fewer operators, maintenance and support staff will be needed. As well, fewer fare inspectors will be required as fare gates will be installed at the LRT stations.

Manconi's email said the city will look to retirements and attrition as ways to keep down the number of layoffs. And some folks hired in dealing with detours in Phase 1 of the $2-billion Confederation Line project could be re-employed in handling detours for Phase 2.

Crabtree said retirement is currently 60 to 80 people annually.

Also, Manconi points out that the city will need to hire additional workers for the light rail system: 70 operators, 15 controllers and 10 support staff.

"The Confederation Line creates approximately 100 new positions, which reduces the overall reduction, and management is committed to making all the position available to our current employees by investing in training, facilities, equipment, etc. to create the opportunities for you to be successful in qualifying for these exciting new opportunities," according to Manconi's memo.

His email also states that all drivers hired since 2015 have been told that fewer operators will be needed by 2018.

Crabtree said he is "exploring all options" in the wake of the news but did not offer specifics.

"We'll do everything to protect our members," he said, adding that he will be meeting with OC Transpo management again in August.