Delta, AirTran and other airlines on Wednesday began sending letters to frequent fliers encouraging them to pressure Congress to regulate oil speculation, which the airlines say is behind the huge spike in jet fuel prices.

Frequent fliers of Delta Air Lines, AirTran Airways and at least 10 other airlines are receiving the missives via e-mail. They encourage the consumers to go to a Web site that has a form memo ready to send to lawmakers.

The site, stopoilspeculationnow.com, lists members of a coalition including airlines, cargo carriers and other groups representing airport executives, unionized employees, corporate travel executives, gasoline dealers, bus companies and others.

The letter, signed by chief executives of the airlines, tells customers oil prices mean "widespread economic pain" and adds, "this pain can be alleviated, and that is why we are taking the extraordinary step of writing this joint letter to our customers."

The e-mails are going out to tens of millions of frequent fliers, according to Air Transport Association spokesman David Castelveter.

It's the latest move in a campaign by airline executives who want the federal government to stem the rapid rise in oil prices. The cost of jet fuel is nearly double what it was a year ago.

Delta's letter is going to about 2 million of its SkyMiles members. Delta and Northwest Airlines, which plan to merge, already asked their employees to contact Congress and say nearly 20,000 letters have been sent from those employees so far.

The letter to customers is "really an unprecedented move," Delta spokesman Kent Landers said.

AirTran's letter is going to about 3 million A+ Rewards members.

"I think this is the sort of thing that can direct attention to at least a potential cause" for the rise in the cost of fuel, said Kevin Healy, AirTran's senior vice president of marketing and planning.

Others dispute what is to blame for the high cost of oil.

Atlanta-based energy exchange InterContinental Exchange in a letter on its Web site says that responsibility for fundamental changes in oil prices "cannot lie with a single exchange, regulator or group of market participants."

And a coalition of financial services associations sent a letter to members of Congress last month saying without speculation, "consumers would likely pay more for energy and commodities." The group also said some of the proposals to tighten regulations would be counter-productive.

"We've been through these battles many, many times before," said Will Acworth, a spokesman for the Futures Industry Association, one of the financial services associations that signed the letter. He said his group is hopeful that congressional committees with jurisdiction over the issue "reach a sensible conclusion."