Relatives of a Maine fisherman killed in the sinking of the Starbound have filed a second lawsuit against the Russian-operated tanker that allegedly hit the fishing boat.

The suit, filed Monday, initiates a case in U.S. federal court in addition to one filed Friday in Canadian federal court.

In the six-page complaint in U.S. District Court in Boston, the widow and children of James Sanfilippo of Thomaston seek $6 million each from the Cypriot owner of the tanker and the Russian operator. The relatives, widow Aimee Lynne Sanfilippo, son Sebastian Joseph Sanfilippo, and stepdaughter Ariana Anne Wadsworth, are also seeking $6 million from the shipping company in Canadian federal court in St. John’s, Newfoundland.

The relatives and the company that owned the Starbound, Atlantic Mariner Inc., filed Canadian lawsuits so the tanker Virgo could be used as collateral for possible damages. The cases seek to prevent the ship from leaving before the case is resolved because the ship is owned and registered by a Cypriot company, A.L.T. Navigation Ltd., and operated by a Russian company, Primorsk Shipping Corp.

David Anderson, a Boston lawyer representing Sanfilippo’s relatives in both cases, said the dispute should be tried in Boston because that’s where the Virgo conducted substantial business with the United States and it’s where most of the Coast Guard investigators are based.

“The case ought to be litigated in New England,” he said.

A Primorsk spokeswoman did not respond to calls seeking comment.

The 83-foot fishing boat sank before dawn on Aug. 5. Its captain, James Marcantonio of Gloucester, Mass., was the only survivor. He described to investigators how a large tanker ran over the ship and kept going, its crew never acknowledging the collision.

Sanfilippo’s body was found floating about 130 miles off Cape Ann, Mass. Two other crewmen, Thomas Frontiero and Mark Doughty, were missing and presumed dead. Doughty lived in Yarmouth.

Criminal charges alleging manslaughter were filed a week ago in U.S. District Court in Washington against the ship’s captain, Vladimir Ivanov, second officer Dmitriy Bogdanov and helmsman Mikhail Gersimenko. An extradition hearing is scheduled Sept. 13.