Argentina's former President Mauricio Macri has been charged with ordering the secret services to spy on relatives of 44 sailors who died when the Ara San Juan submarine sank in 2017.
Judge Marin Bava says Mr Macri has violated the country's intelligence laws by demanding a dossier on the victims' families.
They accuse the Navy of negligence.
Mr Macri, who was president in 2015-19 and is now an opposition leader, says the charges are politically motivated.
"I did not spy on anyone, I never ordered [anyone] in my government to spy on anyone," he said earlier this month.
The victims' relatives say they have been followed, intimidated, and had their phones tapped after accusing the Argentine Navy of negligence in the maintenance of the Ara San Juan submarine.
The vessel was returning from a routine mission when it disappeared 430km (270 miles) off the Argentine coast in the South Atlantic on 15 November 2017.
The wreckage was found only a year later off the coast of Patagonia.
Experts believe the submarine imploded and sank after a technical fault.