Last-minute lobbying of the White House by charter and cargo airlines has delayed-and could jeopardize-new regulations to combat pilot fatigue, according to industry officials.

Issuing strict new rules to replace decades-old limits on pilot work hours and rest periods has been a top priority for the Federal Aviation Administration and its chief, Randy Babbitt. Until a few weeks ago, the FAA was on track to release the revamped rules by an Aug. 1 deadline mandated by Congress.

But the timing and details of an announcement are now up in the air, industry officials said, following direct appeals last Friday by representatives of charter and cargo carriers to the White House Office of Management and Budget, which is reviewing the proposal.

Release of the rules could be weeks or months away, according to industry officials and others familiar with the issues. Many charter and cargo airlines, which under the FAA's proposal would remain subject to the same pilot-fatigue rules as passenger carriers, object to tighter limits on maximum daily work hours and imposition of longer mandatory rest periods.

FAA efforts to keep tired pilots out of the cockpit were revved up following the 2009 crash of a Colgan Air turboprop near Buffalo, N.Y., which killed 50 people. Once investigators determined both pilots were sleep-deprived from long commutes on planes before starting work, Congress mandated tougher FAA rules on pilot fatigue and training.

Missing the Monday deadline sparked complaints from some safety experts, lawmakers, pilot union leaders and a group representing crash victims.

In a statement Tuesday, a spokeswoman said the FAA "is committed to ensuring that airline pilots are fit and rested when they report for duty," and is "working aggressively to complete a new pilot fatigue rule." She declined to elaborate.

A Department of Transportation spokeswoman declined to comment, and White House officials have a standing policy of refusing to discuss pending regulations.

Announced by the FAA in 2010 and based on advances in sleep research, the proposed package aims to base schedules and rest periods on variables such as time of day, as well as the number of takeoffs and landings pilots are scheduled to make during each work day.

The FAA's proposal sought to guarantee pilots at least nine hours of rest between shifts, instead of the eight currently mandated. Maximum work days, including tasks on the ground, generally would be restricted to 13 hours, rather than the current 16-hour limit. But commuter pilots who make multiple landings and takeoffs-particularly late at night or early in the morning-could have that work limit cut to nine hours.

Charter and cargo operators, which often fly long routes overnight and don't rely on predictable daily schedules used by nearly all passenger airlines, argue the changes would be expensive and eliminate necessary flexibility to transport commercial goods and even troops for the Pentagon. Some cargo carriers are pushing to be left out of the current regulations, or want the FAA to craft separate restrictions just for them.

Stephen Alterman, president of the Cargo Airline Association, said new rules "should be enacted at some point in some fashion." But he said the FAA wanted to stick with "a one size fits all" approach that fails to recognize that cargo carriers depend on "a completely different operating model" than passenger airlines.

As part of a stepped-up campaign against the proposal, other cargo-airline officials have enlisted the help of the Pentagon. To appease such concerns, according to industry and government officials, the FAA has reassured charter airlines that they could receive exemptions if the rules ended up adversely affecting flights carrying U.S. troops.

A spokesman for the National Air Carrier Association, some of whose members carry troops and military supplies, couldn't immediately be reached for comment on Tuesday. Earlier this year, the association tried but failed to get Congress to exempt such charter flights from pending FAA pilot-fatigue rules. At the time, the group's president said the proposed changes would have a "disastrous" economic impact on nonscheduled carriers, requiring a roughly 40% increase in the number of pilots on their payrolls.

In crafting its comprehensive proposal last year, the FAA sought to give airlines greater flexibility to allow pilots more hours on the clock, for example, in case of unexpected weather delays. Other parts of the proposal, envisioned to kick in by 2013, were intended to provide unions additional assurances that carriers would be required to establish realistic schedules for pilots. But from the beginning, representatives of cargo and charter carriers stressed that they weren't happy with the trade-offs, and some privately threatened to eventually file suit against the FAA.

The Air Transport Association, whose members account for 90% of U.S. cargo and passenger traffic, has objected to the proposal as overly restrictive and met with White House regulatory officials last week. But ATA also has privately signaled that, with some revisions, it could live with portions of the package, industry officials say. An ATA spokeswoman declined to comment.

The largest North American pilot union, a big supporter of the FAA's efforts, on Tuesday issued a statement expressing "serious concern" about what it called the White House's "unacceptable" role in delaying the announcement of the package.