A pilots' strike at Spirit Airlines prompted the carrier on Monday to extend flight cancellations through mid-week, with shares of rivals moving higher on prospects of more business.

Pilots represented by the Air Line Pilots Association (ALPA) struck on Saturday after last-ditch talks with the discount carrier failed to bridge differences over pay.

Florida-based Spirit said it is offering affected customers flight credits for the full amount of their canceled flights and giving them a $100 future flight credit.

Privately held Spirit operates more than 150 flights per day, primarily to the eastern United States, Latin America and the Caribbean.

Airline shares rose along with the broader market on Monday. But shares of Spirit's most immediate rivals, JetBlue Airways Corp, American Airlines parent AMR Corp and AirTran Holdings Inc, also rose on prospects of additional business.

JetBlue shares were up about 6 percent on Nasdaq. AirTran rose nearly 2 percent and AMR nearly 3 percent on the New York Stock Exchange.

Spirit accounts for less than 1 percent of the overall U.S. market, with about 5.2 million passengers in 2009.

Spirit pilots planned to picket on Monday at Fort Lauderdale, Florida; Detroit; and Atlantic City, New Jersey, its three biggest cities.

The strike at Spirit is the first notable airline strike since Northwest mechanics walked out in 2005. It is being watched closely by unions in contract talks at other airlines.

Spirit is best known in the industry for its super-low fares and for its controversial plan announced in April to begin charging up to $45 for carry-on bags. Most airlines charge for checked bags only.

(Reporting by Deepa Seetharaman and John Crawley)

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