WASHINGTON (Reuters) - A group of U.S. state attorneys general are investigating Expedia Group and hotel chains like Hyatt Hotels Corp and Marriott International Inc for alleged violations of antitrust law in online travel booking, according to a court filing.

The filing in a state court in Utah relates to a dispute originally filed in Texas in which Travelpass accused the hotel chains last year of agreeing with each other, and with online travel groups like Expedia, to not advertise to consumers who searched for another company's hotel.

This means, for example, that a traveler who searches online for a Marriott in Dallas would not be shown advertising for competing hotels, the Travelpass lawsuit alleges.

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The Utah attorney general's office indicated that it and an unspecified number of other state attorneys general were investigating Travelpass' complaints against Expedia and hotel chains.

The chains named in a document filed with the court included Hyatt, Marriott, Caesars Entertainment Corp and Choice Hotels International Inc.

"With respect to the investigation at issue, a multistate group has formed, but other states may be reluctant to join if there is a risk of future disclosure of their confidential communications," the Utah attorney general's office said in the filing.

According to the filing, the Utah investigation was opened in 2017 and remains active.

The case is similar to one in which hotel customers accused hotel chains of conspiring to not compete with one another online. A judge ruled in March that that case could go forward.

Expedia, Caesar's and Choice did not respond to a request for comment. Hyatt and Marriott declined comment.

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(Reporting by Diane Bartz; Editing by Bill Berkrot)