NEW YORK (CNN/Money) - United Airlines became the second major U.S. airline to announce it will try to do away with the traditional paper tickets.

To help spur the change to so-called electronic tickets or "e-tickets," the airline will start charging $20 for any customer who can use an e-ticket but wants to get a traditional paper ticket. That change takes effect Thursday, Aug. 1. The airline estimates that about 70 percent of customers already travel with e-tickets.

United Airlines customers who want to use a paper ticket will have to pay $20 after Thursday.

United hopes to do away with paper tickets by July 2003 for domestic travel and by January 2004 for all travel. The only people who will be able use traditional paper tickets for free are those who booked part of their travel with another carrier that does not have a cross-electronic booking agreement with United. The airline said it will move to increase the number of carriers with whom it has those agreements by the deadlines above.

The move follows a similar announcement by American Airlines, the world's largest carrier, at the end of June. American raised the charge for a paper ticket at that time from $10 to $20. United, the world's No. 2 airline, had not charged for the paper tickets before this announcement.

The airlines have been looking for ways to cut their distribution costs. Earlier this year they eliminated most travel agent commission that they paid.

Paper tickets are an expensive and somewhat cumbersome way to book passengers. The tickets all have serial numbers and they had to be audited and accounted for and cleared almost like a personal check from a bank. While neither United nor American would release details on their costs of handling paper tickets, David Stempler, president of the Air Travelers Association, said $20 is probably a relatively accurate and fair representation of that cost.

The paper tickets had the advantage of letting passengers move from one airline to another if they were bumped off their flights. But even that process is becoming easier to handle electronically. The fact that the customer normally gets a printed itinerary with an e-ticket satisfies most fliers, even those who are generally uncomfortable with adopting new technology, said Stempler.

"Traditionally when you went to hotels or car rental, you had a reservation but no ticket," Stempler said. "I like to have paper tickets to be able to move quickly around airports and change flights, but if you lost it, it was a major pain. You don't have to worry about losing an e-ticket."

Shares of United Airlines owner UAL (UAL: up $1.31 to $6.09, Research, Estimates) were up more than 25 percent in Monday trading.