The unions representing train operators and signalling workers at Canadian Pacific Railway Ltd. have served the company with notice of a strike action.

The Teamsters Canada Rail Conference and the International Brotherhood of Electrical Workers have told CP Rail they will be in a position to strike as of 10 p.m. ET Tuesday.

In a statement issued Saturday, the unions accused the company of "refusing to negotiate seriously," after workers rejected its latest contract offer on Friday.

"CP is offering more of the same contract language that workers just voted to reject a few hours ago," TCRC president Doug Finnson said.

"The company clearly isn't serious about reaching a negotiated settlement and delivering on their promise to do right by their employees."

An IBEW representative quoted in the same statement said CP has "continually changed directions during negotiations," giving no indication that a settlement was possible.

"We have given CP every reasonable opportunity to negotiate and avoid a strike, but sadly that has led us nowhere," said Steve Martin, senior general chairman from IBEW System Council No. 11.

The unions said they are committed to working with federal mediators to reach a settlement, and they will "remain at the bargaining table until the May 29 strike deadline and beyond."

In its own statement, CP said it has "commenced its work stoppage contingency plan" and will work toward a safe wind-down of operations.

"CP will continue to meet with the TCRC and the IBEW in the hopes of reaching agreements that are in the best interests of the entire CP family, its customers, shareholders and the broader North American economy," the railway said.

Via Rail Canada, southern Ontario transit operator Metrolinx, and the BC Rapid Transit Co. have all said a strike at CP Rail would result in disruptions, although the unions said Saturday that commuter train services would not be affected by a Teamsters strike.

CP Rail train crews have engaged in two strikes in the past few years: In 2015, they ended a brief walkout and agreed to arbitration after the Harper government warned of back-to-work legislation; three years earlier, federal back-to-work legislation was enacted to end a 10-day strike.

About 3,000 members of the TCRC voted roughly 98 per cent against the company's most recent offer Friday. The IBEW, which represents some 360 signal and communications workers, voted about 97 per cent against the offer.

The results came after the federal government intervened last month to force union members to vote on the company's offer, ending mediated talks between the railway and the two unions. Union negotiators had recommended that their members reject the offer.