United Airlines said Friday it will start requiring minimum stays for nearly all domestic coach seats beginning in October. It is also raising its cheapest fares by as much as $90 one-way.

The second-largest U.S. carrier said the moves are among a number of changes, including flight and job cutbacks, it is making to combat record high fuel prices.

The Chicago-based airline has been among the industry's most aggressive in pushing fares and fees higher in recent months, and those efforts have often been matched by other carriers. The industry is scrambling to raise revenue in a fight to forestall what is projected to be a record multibillion industrywide loss this year.

Starting Oct. 6, most of United's economy-class fares will require a one- to three-night or weekend-night minimum stay, spokeswoman Robin Urbanski said. The policy does not apply to fliers in other classes.

The new rules are bound to be unpopular with business travelers who prefer to catch a flight out early in the morning so they can be back home in time for dinner.

"They'll push back big time," said Mike Boyd, a Colorado-based aviation consultant. "It's one thing to simply raise fares. It's quite another to do it by imposing restrictions that appear to make it harder to conveniently fly."

Major carriers scrapped most minimum-stay rules — put in place largely to discourage big-budget corporate travelers from snatching up the cheapest seats — at the start of the decade, although United and other airlines recently started bringing the overnight rules back piecemeal.

Friday's changes are far more sweeping because they also apply to highly competitive routes where United goes head-to-head against lower-cost rivals such as Southwest Airlines and JetBlue Airways.

"What we did this week was almost across the board," Urbanski said. "At the end of the day, it's all about improving our profit as we combat these record high fuel prices."

How long passengers have to stay under United's new minimum-stay policy will depend on the destinations involved, the price of the ticket and the length of the flight.

For example, travelers booking the cheapest seats between Chicago and Minneapolis or Boston and San Diego will now be forced to stay three nights or the entire weekend, Urbanski said.

United also has raised its lowest fares by $1 to $90 one-way, meaning the least expensive available United ticket will now cost travelers $69 to $199 one-way, depending on the length of the flight.

For example, the cheapest one-way ticket for the 770-mile flight from Denver to St. Louis now costs $99, up from $89 before. A bargain ticket for a longer flight like Austin, Texas, to Los Angeles — a journey of nearly 1,240 miles — now costs $139, up from $79 one-way, Urbanski said.

United and US Airways last week joined American Airlines in charging passengers $15 to check their first piece of luggage. Like a number of other carriers, United also tacks on a fuel surcharge onto many tickets that can range from $5 to $75 on-way.

Kevin Mitchell, chairman of the Business Travel Coalition, said that as long as fuel prices remain high, United and other carriers have little choice but to raise fares and find other ways to raise cash.

"Is there going to be a price to pay for it in terms of traveler backlash? The answer is yes," he said. "But there are simply no good answers right now. ... We have a full-blown crisis heading for a catastrophe."