The workers apparently began intentionally slowing down the screening process on Thursday over the issue of scheduling changes.

Garda Security won an injunction from the Canada Industrial Relations Board that prohibits workers from slowing down on the job. The injunction came after some passengers complained about waiting for up to three hours to pass through security and about waiting for two hours on the tarmac.

The security staff returned to their normal work levels Thursday afternoon, but flight delays continued Thursday night and into Friday.

Among those caught up in the delays caused by the work to rule was Treasury Board President Tony Clement. "Yes, I'm currently stuck on plane on the tarmac," Clement tweeted on Thursday evening.

Garda was recently awarded a new five-year contract by CATSA worth approximately $650 million for screening services in Ontario airports which is due to commence Nov. 1, 2011.

— With files from The Canadian Press