Southwest says WestJet requested "significant changes" to a 2008 codeshare agreement so Southwest has decided to terminate the pact.
"Southwest cannot agree with the modifications to the confidential agreement," the airline says.
The agreement between Dallas-based Southwest and Calgary-headquartered WestJet initially was to be implemented by the end of 2010, but had been delayed beyond that deadline.
In the interim, WestJet stated a couple of weeks ago that a codeshare with Delta could precede implementation of WestJet's agreement with Southwest, and that appears to have been one of the factors that derailed the Southwest-WestJet pact.
Southwest said April 16 that WestJet sought to modify the agreement for connecting service over the past several months and has since "reaffirmed and clarified its request."
"We prefer the existing terms of our agreement with WestJet," says Bob Jordan, Southwest's executive vice president of strategy and planning. "Upon reviewing the number of changes that WestJet has requested, we have decided that it is in the best interest of both parties to move forward independently."
He adds: "We remain interested in exploring the possibility of one day offering service to Canada if it makes sense for Southwest and for our customers. That would not rule out furture codeshare relationships with Canadian carriers, or flying north of the border ourselves."
WestJet transitioned to the SabreSonic reservations system late last year -- a move that the airline said would enhance its ability to enter into codeshare agreements.
WestJet didn't immediately reply to a request for comment about Southwest's action.
As a precursor to implementation of the airlines' codeshare agreement, Southwest enabled consumers to book WestJet flights on Southwest.com.
There's been no word from Southwest yet on whether that functionality will be dropped.