AECL employees are bracing for up to 900 layoffs as details emerge about likely job cuts in the wake of the federal government's deal with SNC-Lavalin.

Ottawa announced Wednesday that it reached a tentative deal with the Montreal-based engineering firm to sell the Crown corporation's commercial reactor development and repair division for $15 million.

One of the unions for AECL workers, the Society of Professional Engineers and Associates, condemned the sale and said it will result in a "hollowed out company."

SNC says it will create a new division called Candu Energy, which will include the AECL reactor division's three former business lines and keep at least 1,200 jobs as it assumes ownership.

AECL's chief executive Hugh MacDiarmid told staff in a memo to expect between 800 and 900 layoffs.

On Thursday, a memo obtained by CBC News from the union to members revealed details about who will be getting pink slips over the coming months.

The memo said AECL sent a "notice of mass termination" to Labour Minister Lisa Raitt that indicated up to 900 jobs are on the chopping block.

Staff affected include up to 310 scientists and engineers, 155 technologists, 240 accountants and project managers, 45 employees who specialize in design drafting and 150 people in management.

"Although we all knew that an announcement of the sale was pending, and we all heard the rumours about staff reductions, we were as surprised as anyone by the extent of the staff reductions contemplated," the union's vice-president Michael Ivanco wrote.

The layoffs will happen between July and September, but the union says it's going to try to prevent some of them.

"We will be meeting to discuss ways of possibly reducing the extent of layoffs and we intend to pursue arrangements such as work sharing to try to reduce layoffs," the memo said. Ivanco said the union has already talked to senior representatives at SNC about how to mitigate job losses.

The Conservatives announced in May 2009 that they planned to spin off AECL's commercial reactor business from its research division. SNC was the sole bidder to meet Ottawa's conditions for buying the financially troubled Crown corporation.

The deal is expected to be completed this fall.