German antitrust regulators gave a stiff warning to Priceline Group Inc.’s Booking.com, saying they are likely to ban the online reservation site’s best-price deals with hotels.

Booking.com and Expedia Inc. are using the [rate parity] clauses despite a 2013 order by Germany’s Federal Cartel Office telling another online travel company not to stop hotels from giving better prices to competitors or directly to customers, Bundeskartellamt regulators said in a statement Thursday.

“The Bundeskartellamt intends to forbid Booking.com, by far the largest hotel portal in Germany, from further use of the best-prices clauses,” regulators said in the statement. “The ongoing procedure against Expedia continues.”

The cartel office said it rejected Booking.com’s proposal to settle the case as insufficient. The company also made offers to French, Swedish and Italian antitrust regulators last year to end their parallel probes. The U.K. must decide whether to re- open a probe into Booking.com, Expedia and InterContinental Hotels Group Plc after a court overturned a planned settlement.

Booking.com declined to immediately comment.

Hotel Reservation Service Robert Ragge GmbH isn’t appealing a court challenge against the Bundeskartellamt order that it lost in January, the cartel office said. The order told HRS to delete best-price clauses from its contracts.

–With assistance from Cornelius Rahn in Berlin.

 This article was written by Aoife White from Bloomberg and was legally licensed through the NewsCred publisher network.

Photo Credit: The Maritim Hotel in Frankfurt, Germany. slack12 / flickr.com