Some airlines, hotels pulling the plug on discount websites

Customers bargain-hunting for the best online travel deals may find fewer options than before. Third-party sites like TripAdvisor and Expedia are featuring less options because airlines and hotel are holding back their business.

"What you're seeing is, when you're looking at the total amount of money that these online agencies are booking every year, we're talking about $51 billion in bookings. The airlines and hotels are saying, 'We want some of that,'" CBS News travel editor Peter Greenberg said Friday on "CBS This Morning."

Sen. Chuck Schumer Monday called on the Department of Transportation to investigate airlines that won't allow their fares on other sites. According to the Travel Technology Association, this move by the industry could cost consumers more than $6 billion a year.

"Law of supply and demand," Greenberg said. "If you restrict the opportunity for comparison shopping you have a problem."

The probe would supplement an ongoing investigation, recently announced by the federal government, looking into possible collusion by the airline industry to slow their growth and keep airfares high.

Greenberg pointed to recent history to explain why companies are beginning to pull out from online travel agencies (OTAs).

"When they started these OTAs ... it came at a time when airlines were in big trouble financially. So they went to them and said, 'Hey, let us sell all your unsold inventory. We'll be your friends," Greenberg said. "Airlines are doing better now than since the Wright brothers. They don't think they need them."

So far, Greenberg said, Delta Air Lines has removed their schedule and fair information from over 12 different sites including TripAdvisor, Hipmunk Inc. and CheapOair.com.

The Lufthansa Group, which includes Lufthansa, Brussels Airlines, Australian Airlines and Swiss, announced a plan to charge $18 for travelers who book on third-party sites.

In a statement to CBS News, Lufthansa said: "The implementation of the Distribution Cost Charge aims at broadening, not limiting, Lufthansa's distribution via third party channels and other travel industry partners which eventually enables them to market more products and features that Lufthansa is currently investing in."

Delta did not return CBS News's request for comment.

This isn't the first time drama between airlines and OTAs has played out. In 2011, American Airlines removed listings from Orbitz.

"It's about consolidation and distribution and revenue streams," Greenberg said.

Hotels are stepping onto the battlefield too. Greenberg said a variety of hotels are turning away from third-party sites and may not honor existing reservations booked through OTAs.

"The big brands like Hilton, Hyatt, Marriott, Starwood -- they charge high franchise fees. Now the owners are upset, who are operating those hotels. Why? Because they are getting most of their bookings online from people like Expedia and Travelocity and they have to pay them a commission," Greenberg said.

For travelers worried they'll have their work cut out for them trying to find the best deal, Greenberg offered one piece of advice: Pick up the phone, and call the individual hotel. Customers may be able to find better deals that way.

"About 52 percent of all the inventory is online. What about the other 48 percent? That's what they hold back. You should have that conversation even if we weren't doing this particular story," he said.