The charge will apply to customers who buy nonrefundable domestic economy tickets and who aren't "premier"-status or higher members of United's frequent-flier program, or of a similar airline plan at one of its marketing partners, the Chicago-based carrier said today in a statement. United expects to produce $100 million in cost savings and new revenue.

United and other airlines are trying to trim costs and increase sales to help offset a 49 percent jump in jet-fuel prices over the past 12 months. A baggage charge allows the carrier to collect more revenue without raising its fares higher than those at competitors.

"Our customer research shows that only about one in four customers check a second bag," Executive Vice President John Tague said in the statement.

The policy takes effect May 5 on flights within the U.S., Canada and parts of the Caribbean. It applies to tickets purchased today and after. For all customers, the charge to check up to four additional bags will be $100 each, the airline said. Previous charges ranged from $85 to $125 per bag.

UAL fell $1.30, or 3.2 percent, to $39.84 at 10:10 a.m. New York time in Nasdaq Stock Market composite trading.