The ruling Law and Justice party is led by a Walesa opponent, Jaroslaw Kaczynski. He claims Poland's democracy was largely shaped by people linked to the ousted communist system and needs an overhaul.
Walesa is being portrayed by ruling party leaders as a collaborator of the communist secret police. The investigation is linked to communist-era documents found last year. Citing tests by handwriting experts, prosecutors allege the papers include reports Walesa wrote for secret security agents from 1970-76.
During questioning by prosecutors of the National Remembrance Institute, which investigates Nazi and communist crimes against Poles, Walesa denied he wrote or signed the documents and said they had been fabricated.
Walesa, 73, served as Poland's president from 1990-95. Allegations that he was a secret security collaborator codenamed "Bolek" first emerged in the 1990s. He vehemently denied the assertion and a special court cleared him in 2000.
Deputy Prosecutor General Andrzej Pozorski said Tuesday an investigation into the veracity of Walesa's statements was opened June 29. It relates to his testimony about the recently found documents and to Walesa's earlier statements.
No timeline has been given for the investigation.