The threatened lockout of workers at the two largest Canadian railways began at midnight on August 22, threatening to cripple critical supply chains.

BBC News reports that Canadian National Railway (CN) and Canadian Pacific Kansas City (CPKC), locked out nearly 9,300 workers after failing to clinch a late deal with the Teamsters union.

Read More: Impacts of Canada Rail Strike Would Be Felt Across Country's Supply Chains

After months of talks, the increasingly bitter negotiations, regarding working conditions such as shift scheduling and fatigue provisions, ended on the evening of August 21, CBC reported, with both sides accusing the other of refusing to negotiate seriously.

“Without an agreement or binding arbitration, CN had no choice but to finalize a safe and orderly shutdown and proceed with a lockout,” CN said in a statement.

“CPKC is acting to protect Canada’s supply chains, and all stakeholders, from further uncertainty and the more widespread disruption,” CPKC said, adding that binding arbitration was the only "responsible" way to move forward.

Paul Boucher, president of Teamsters Canada Rail Conference, said the railways had "shown themselves willing to compromise rail safety and tear families apart to earn an extra buck".

"The railroads don’t care about farmers, small businesses, supply chains, or their own employees. Their sole focus is boosting their bottom line," he said.