Portugal's Journalists' Union says an injunction barring a Portuguese media group from reporting on a corruption investigation into a former prime minister is "a grave precedent."

The labor group noted Thursday that press freedom is protected by the constitution and offered legal aid to journalists hindered by the ruling.

A court issued the gag order Tuesday at the request of Jose Socrates, who was Portugal's center-left Socialist prime minister from 2005 to 2011. Arrested a year ago on suspicion of corruption, money-laundering and tax fraud, he was held in jail until last month. Prosecutors are weighing whether to formally charge him.

Cofina Media group, which owns newspapers, magazines and a cable TV channel, has published numerous exclusive stories on the investigation. It said it intends to appeal against the injunction.