Deutsche Telekom, Vodafone, Telefonica Deutschland and 1&1 Drillisch, a unit of United Internet, can participate in the auction that will begin on March 19, the regulator said.

The regulator added the auction date could be changed due to ongoing legal proceedings.

Germany's three main network operators - Deutsche Telekom, Vodafone and Telefonica Deutschland - are all suing the regulator to determine the legality of new preconditions for participating in the auction.

Germany stipulated that bidders for 5G mobile frequencies must invest to expand the country's mobile network and potentially allow new entrants, like United Internet, to use their infrastructure.

(Reporting by Riham Alkousaa and Emma Thomasson; Editing by Thomas Seythal and Mark Potter)