A federal judge has placed a preliminary injunction to stop US Airways pilots from intentionally delaying flights.

US Airways sued the pilots late in July after their June on-time rating was placed last among large airline corporations.

U.S. District Court Judge Robert J. Conrad ruled Wednesday that the pilots' union in fact engaged in an illegal slowdown, The Associated Press reports.

The disruption caused by the 2005 merger between US Airways and American West is thought to be the main contributing factor to the pilots' frustration. The pilots from the two groups still operate under separate union contracts and there is often friction between the two groups on seniority rankings.

Conrad's ruling found the union has expressly tied the success of their 'fight' for a new contract to actions by their member pilots that would slow down the airline but could be cloaked by (a) safety campaign, The Wall Street Journal reports.

Conrad found that the majority of delays were among the old US Airways pilots, or so called East pilots. Pilots within this group were accused of slow taxiing, unnecessary fatigue calls, and delaying completion of online trainings. Conrad found that of the 897 pilots who did not complete the training on-time, only one was from the former American West company. As a result, the Federal Aviation Administration gave the pilots an extension, as the pilots who did not complete the training would not be allowed to fly.

The pilots, who are part of the US Airline Pilots Association (USAPA), deny any wrong doing. USAPA claims that the suit is a way to save money through postponing contract negotiations. President of the USAPA, Michael Cleary, was the only named defendant in the case, although there is insufficient evidence to hold him personally responsible for the hold-ups.  

If the pilots do not yield to the primary injunction, they will face further legal action, including the possibility of fines.

US Airways has not commented on the case, rather sending an email to employees after the case closed.

Thanks to everyone for the amazing job you did to ensure our customers were taken care of while this illegal activity was taking place. We're happy to have it behind us, the email states.