During the Cold War, hundreds of thousands of citizens in communist countries reported on their neighbours and co-workers.
When he resigned, he apologised for his actions and admitted he had hurt the Catholic Church.
Last month, a judge ruled that Wielgus will have a chance to clear his name after he asked a special vetting court to accept his case, saying secret agents had blackmailed and harassed him into co-operating.
Wielgus follows a string of government officials who have turned to the court to clear their names since Jaroslaw Kaczynski, the Polish prime minister, launched a crusade to remove former communists and collaborators from public life.
Cardinal Jozef Glemp, who Wielgus was to have replaced, was returned to the position of archbishop until Nycz was named as his replacement.