CHICAGO—United Airlines pilots, still simmering over what they call "inadequate" training and "compromised safety" stemming from United's 2010 merger with Continental Airlines, have ratcheted up their pressure on the carrier by circulating to members of Congress a highly critical 101-page report by their union.

The document, dated Nov. 10, lambasts United for using only individual, computer-based training to help United pilots absorb a "large volume of procedural changes, some of which are quite complex," without including classroom work or practice sessions in flight simulators.

"United's training regime is the equivalent of the Ringling Brothers Circus introducing a new trapeze routine and training the artists via computer," says the document, prepared by the Air Line Pilots Association branch that represents the 6,000 United pilots.

The report alleges that new cockpit procedures imposed on United crews are causing stressed pilots to report higher-than-normal numbers of safety lapses, including instances of nearly forgetting to lower landing gear before touchdown. Other pilots, according to the report, have been so distracted and unfamiliar with the changes that they failed to properly follow taxi instructions on the ground, while still others took themselves off duty because they felt they weren't fit to fly.

"These claims are baseless and are an attempt by the United unit of ALPA to influence contract negotiations under a false guise of safety," United Continental Holdings Inc. said in a statement Monday, citing a "history" of union steps "to disrupt the operations of the airline."