BRUSSELS — The European Union’s top court ruled Monday that national maritime authorities cannot impound ships involved in search-and-rescue work on suspicion that they might be overloaded due to the number of migrants they plucked from the sea.

The European Court of Justice ruling came in response to an appeal by German migrant aid group Sea-Watch. Two of the German group’s ships were forced to undergo inspections in Sicily in 2020 after disembarking migrants for taking aboard more people than they were authorized to carry.

Italian harbor authorities also considered that the ships were not certified for search-and-rescue missions.

But the court said that rescued people “must not be taken into account when verifying whether the rules on safety at sea have been complied with. The number of persons on board, even if greater than that which is authorized, cannot therefore, in itself, constitute a ground for a control.”

The Luxembourg-based ECJ also said national port authorities have the right to inspect ships to assess whether rules on working conditions, health and safety, and the environment are being respected.

But it added that they do “not have the power to demand proof that those ships hold certificates other than those issued by the flag state,” which in the case of the Sea-Watch vessels was Germany.

Sea-Watch described the court decision as a victory that means that port authorities can’t arbitrarily detain ships and prevent them from doing their work.

“The ruling provides clear legal security for NGOs and is a victory for sea rescue. In the future, ships will thus continue to do what they do best: Rescue people instead of being arbitrarily stuck in port,” the organization said in a tweet.

Neither the EU nor any of its 27 nations are actively searching for people in danger in the Mediterranean Sea, where more than 1,000 people have died or are missing so far this year, many of whom tried to reach Europe from North Africa in unseaworthy smugglers’ boats.

But ships are bound by international law to respond to any distress call near them.

Most Europe-bound migrants hope to reach family or find work, but many of them are denied asylum because they fled poverty and not persecution or war.

Migration is a key issue in Italy’s early parliamentary election on Sept. 25. Right-wing League party leader Matteo Salvini has promised to take a hard line on migration if his party comes to power in a center-right alliance.