In a rare move, federal authorities have seized the cargo ship involved in last month’s record-breaking cocaine bust at the Port of Philadelphia, and said Monday they are weighing forfeiture proceedings against its owner, one of the world’s largest shipping conglomerates.

Court records unsealed this week indicate that a U.S. magistrate judge authorized the seizure of the MSC Gayane on June 26 — a week after investigators discovered its illicit cargo, nearly 20 tons of the drug believed to be worth more than $1 billion. Agents delivered the seizure warrant to the ship’s captains on July 4, the documents show.

Prosecutors have not indicated whether they will try to take permanent possession of the ship, the length of three football fields, or pursue financial penalties against its owner, Geneva-based Mediterranean Shipping Corp. (MSC).

Still, U.S. Attorney William M. McSwain said his office’s decision to seize the craft was as warranted as it was unusual.

“When a vessel brings such an outrageous amount of deadly drugs into Philadelphia waters, my office and our agency partners will pursue the most severe consequences possible against all involved parties in order to protect our district — and our country,” he said in a statement.

Justice Department efforts to seize ships hauling illicit cargo are not unprecedented. In May, federal prosecutors in Manhattan initiated forfeiture proceedings against a shipping vessel caught exporting coal from North Korea in violation of American law and international sanctions.

So far, prosecutors in Philadelphia have not accused MSC of any wrongdoing. But the seizure of the Gayane is only the latest setback for the company in the United States this year.

Customs agents discovered about 1.6 tons of cocaine on another of its cargo ships, the MSC Carlotta, in February as it pulled into the Port of Newark.

A month later, law enforcement officials found another half-ton of cocaine in 13 large duffel bags housed in a shipping container off-loaded in Philadelphia from the MSC Desiree.

Authorities touted that bust at the time as the largest cocaine seizure at the city port in two decades. That record lasted for less than three months, with the Gayane discovery on June 16.

Since then, U.S. Customs and Border Protection has temporarily suspended the company’s participation in a fast-track screening initiative for trusted freighters — a program akin to the Transportation Security Administration’s PreCheck program for frequent travelers at airports.

For now, the Gayane remains anchored in the Delaware River, and its crew’s access to the ship remains restricted, as it has been since agents conducted their three-day search of the ship last month.

The massive cocaine haul was hidden in shipping containers and stashed among wine, vegetable extract, Chilean dried nuts, and scrap metal from the United Arab Emirates.

Prosecutors said Monday that the ship’s legitimate cargo — which was bound for Europe, Africa, and Asia — was not subject to the court’s seizure order.

Six members of the crew, all from Eastern Europe or Samoa, have been charged with violations of maritime drug smuggling laws and remain in custody in Philadelphia.

At least two have confessed to helping smuggle the drugs aboard, according to court filings that have since been sealed. They said the cocaine came from 14 boats that separately approached the Gayane as it journeyed between Peru and Panama while en route to Philadelphia.

Federal prosecutors have declined to discuss their investigation and have requested judges seal many of the records surrounding the case. Sources familiar with probe said that a grand jury is continuing to hear testimony about the Gayane’s journey.

An MSC official declined to comment on the seizure of the ship Monday.

“Unfortunately, shipping and logistics companies are from time to time affected by trafficking problems,” the firm said in a statement last month. “MSC has a long-standing history of cooperating with U.S. law enforcement agencies.”