Updated from 12:52 p.m. EDT

US Airways

(U)

announced a fare sale Tuesday, offering 25% discounts on many off-peak fares in North America and the Caribbean through fall.

US Airways called the sale the airline's traditional summer promotion. It coincided with the height of an especially frenetic season of air travel.

The discounted fares, which must be made 14 days in advance, require roundtrip travel and usually require a Saturday night stay, will run from July 21 to December 15, the company said.

It was not immediately clear whether other airlines would follow suit.

Customers who purchase their tickets online through the company's Web site, will receive an additional 5% off.

Shares of the Arlington, Va.-based company finished up 1 1/16, or 3%, at 40 3/4.

US Airways has

agreed to merge with

UAL

(UAL) - Get Report

, the parent of No. 1 U.S. carrier

United Airlines

, for $4.3 billion in cash. UAL will also assume $1.5 billion of US Airways debt and $5.8 billion in aircraft operating leases.

United did not immediately return a call, and it was unclear how other carriers would react to the discounts. But rival airlines routinely match such sales.