A union representing SNC-Lavalin Group Inc. engineers has filed a complaint with the national labour board alleging bad-faith bargaining after a subsidiary ordered workers back to the office full-time with one business day's notice.

On June 2, Candu Energy Inc. mandated all employees to return to the workplace as of last Monday, a requirement the Society of Professional Engineers and Associates (SPEA) says amounts to a negotiating tactic amid a rotating strike launched May 29 at Ontario's Darlington nuclear plant, which Candu is refurbishing.

In a copy of the memo obtained by The Canadian Press, SNC executive vice-president Bill Fox reminds workers that a hybrid work model proposed to start Sept. 12 is "on the table," meaning that the abruptly announced "full-time in-office working policy could change when bargaining concludes."

Union spokesperson Denise Coombs said SNC-Lavalin's sudden move to bring roughly 900 engineers, scientists and technicians back to the office five days a week has sent them scrambling for living arrangements after more than two years of remote work. It amounts to an unfair labour practice given the bargaining context, according to the union's filing to the Canada Labour Relations Board.

"We all knew it would take time for people to reorganize their lives, obtain child care, move back to the city, all those things," Coombs said in an interview.

Both sides had agree on Sept. 12 as a start date for hybrid work, she said. The key points of discussion were whether it should be three days a week or two and a half on average, as well as salary, benefits and whether the union would be allowed to publicize certain internal documents.

The union received an offer for a collective agreement at a June 2 meeting, where the company also gave it a heads-up on its imminent back-to-the-office memo, Coombs said.

"The clear implication was that if SPEA did not accept Candu's June 2nd offer, Candu would retaliate and force employees to return to the office with just over one business day's notice and on a five-day per week basis," the filing states.

"We were gobsmacked," Coombs said.

SNC spokesperson Harold Fortin said the company hopes to reach a "fair, equitable and competitive agreement" with the Candu workers, who have been refurbishing reactors at the Darlington Nuclear Generating Station.

"With changes in provincial restrictions, people are becoming more accustomed to being together in indoor spaces and it is time to return to the physical workplace," he said in an email.

Fortin cited collaboration, training and integration of new hires among the benefits of returning to a shared workspace.

The Montreal-based company declined to comment on negotiations over the collective agreement, which expired Dec. 31.

Tensions between SNC and the union prompted Ontario Power Generation and Bruce Power to warn they will have to consider "alternate arrangements" if the two parties cannot provide "certainty" in their services.

"This letter should not be taken as support for either side as we respect the collective bargaining process, and at the same time expect to be treated as customers, not a negotiation point," OPG CEO Ken Hartwick and Bruce Power CEO Michael Rencheck said in a letter to SNC and the union dated Tuesday and obtained by The Canadian Press.

The provincial Crown corporation owns the Darlington nuclear plant, and SNC provides services to Bruce Power, including ongoing reactor refurbishment at the Bruce Nuclear Generating Station on Lake Huron.

Between 30 and 70 Candu workers daily have been conducting work stoppages out of roughly 700 on a strike rotation, the union said.

“Now we’re preparing for a large dispute," said union spokesperson Michelle Duncan. "We’re planning on a full-blown escalation.”