SASKATOON -- A labour dispute has interrupted work at two Saskatchewan uranium facilities.

Cameco (TSX:CCO) shut down production at the McArthur River mine and Key Lake mill when the union's strike deadline early Saturday morning approached.

Cameco says it issued a lockout notice earlier in the week to assure a safe and orderly shutdown of its facilities and continued protection of the environment.

The United Steelworkers Local 8914 represents the 535 affected workers at the sites.

It says issues in the dispute include pensions, benefits and compensation for working in remote regions.

The workers' previous contract expired at the end of 2013.

"After all the efforts made to find a fair resolve to bargaining, it was incredibly disappointing that in the final hours leading up to the deadline, the company's only concern was to demand 24 additional workers to be added to the essential services list to finish off a production raise underground over the next few weeks," the union's lead negotiator, Mike Pulak, said in a news release.

Cameco said the facilities will be maintained in a safe shutdown state by salaried Cameco employees and unionized personnel under an essential services agreement with the union.

Pulak noted the union will be complying with essential services under the Canada Labour Code, and will ensure there is no danger to safety or health of the public or environment as a result of the dispute.

In July, the company and union jointly applied for conciliation under the code.

Cameco said it presented its final offer to the union bargaining committee on Thursday and requested that it be submitted to the union membership for a vote.

"The union bargaining committee rejected the offer and advised Cameco that it would not present it to the membership for a vote," the company stated in a news release.

Cameco said it began flying unionized workers to their home communities on Friday evening "in order to assure safe and orderly departure of unionized employees from the remote northern sites."

It said the work stoppage is not expected to affect the company's 2014 uranium delivery commitments to customers.