An international court has refused to block Mexico from trying to collect a $96m tax and customs penalty from Belgian group Jan De Nul in a nine-month dispute over a seized dredger.

Luxembourg went to the International Tribunal for the Law of the Sea (ITLOS) to secure a series of undertakings following the “exorbitant” fine imposed after the 8,015-gt dredger Zheng He (built 2010) called into the Mexican port of Tampico.

The dredger with 36 crew on board had requested to dock in Tampico for three to four weeks to await instructions, crew changes and new provisions, according to a ruling.

But trade officials seized the Luxembourg-flagged vessel on 1 November last year on the grounds that it should be treated as an “import” and contravened customs laws, Luxembourg said in its submissions.

The Zheng He, a cutter suction dredger, is owned by European Dredging Co, a Luxembourg subsidiary of shipowner Jan De Nul, which was handed the fine.

Lawyers for Luxembourg, which brought the case, told the court that it was seeking a ruling that Mexico would not be able to seize any other ships from the Jan De Nul Group over the dispute. It sought other undertakings, including assurances over crew changes and ownership of the vessel.

But the panel of judges rejected the bid by Luxembourg by 22 votes to one because there was no “imminent risk” of “irreparable prejudice” to the shipowner while the legal dispute in Mexico played out.

Luxembourg claims tax and customs demands had already been declared null and void by the Mexican courts. But the Mexican government, which opposed Luxembourg’s move, said that the case was still being considered by a higher court.

ITLOS is an independent body established by the United Nations Convention on the Law of the Sea to rule on disputes between the 169 states that have signed up.

Its decisions are final and binding, but the tribunal has no enforcement powers. It has previously awarded compensation and reinforced the right of vessels to operate at sea without interference from foreign governments.

In 2019, it backed Panama in the case of the arrest and detention of a bunker tanker by the Italian state 21 years earlier and awarded $285,000 compensation plus interest.

The Marshall Islands has brought a claim to the court against Equatorial Guinea over the alleged illegal detention of Ray Car Carriers’ 299,995-dwt VLCC Heroic Idun (built 2020) on suspicion of attempted oil theft and filing false piracy reports.

Its 26-strong crew was held for almost nine months in Equatorial Guinea and Nigeria before a plea deal was agreed to allow their return home.

Charges against the crew were dropped in return for the ship accepting a single criminal charge, an apology and a multimillion-dollar financial settlement.