If the vessel was Spanish or was removed from that country's waters, any treasure would belong to Spain, said James Goold, an attorney representing the government.
"It's a very well established principle under Spanish, U.S. and international law that a government such as the kingdom of Spain has not abandoned its sunken ships or sunken property, and that a company like Odyssey Marine Exploration may not conduct recovery operations without authorization by the government," he said.
"The kingdom of Spain has not authorized any such operations by Odyssey, and by these legal actions it will see the return of any Spanish property Odyssey has recovered," Goold said of the claims filed Wednesday.
"Spain has decided to go to (the) courts to claim its right in case the discovery is Spanish," Susana Tello, Culture Ministry spokeswoman.
Phone messages and an e-mail left for Odyssey officials were not immediately returned early Thursday.
Odyssey announced two weeks ago that it had discovered a shipwreck containing 500,000 gold and silver coins somewhere in the Atlantic Ocean. The Tampa-based company said the site was outside any country's territorial waters but would not give the exact location or name of the ship.
Odyssey has said that the ship was not in Spanish territorial waters and was not the HMS Sussex, a shipwreck that Odyssey recently got permission from the Spanish government to search for in the Strait of Gibraltar.
But Spain has called the new discovery suspicious and said the booty may have come from a wrecked Spanish galleon.
In Britain, the find generated press reports that Odyssey had salvaged the wreck of the long-sought British vessel Merchant Royal, which sank in bad weather off England in 1641. Odyssey has not confirmed or denied these reports.
Spain is using the U.S. law firm Covington & Burling, which has represented Spain over shipwreck cases before, including the recovery of material from two ships, Juno and La Galga, in a 2000 court case. The Spanish government won the case at that time.