Cahuzac, who has pushed for a stronger fight against tax evasion, has categorically denied ever having had a foreign bank account.
But Médiapart, an investigative news website that first reported his alleged Swiss account earlier this week, on Wednesday buttressed its findings by releasing a tape recording of a telephone conversation from 2000.
The recording appears to show Cahuzac discussing with someone the fact that he has a UBS account that he wants to close.
Cahuzac asks if the only way he he can close the account is to go there (presumably to Switzerland) which is “damn annoying”.
He talks about the possibility of becoming a municipal mayor and not wanting the “least ambiguity” about his finances.
Prime Minister Jean-Marc Ayrault told RTL on Thursday that he continued to have“complete confidence” in his budget minister.
Asked about the Médiapart telephone recording, Ayrault said he had not had the time to learn about it.
But the prime minister repeated his faith in Cahuzac, noting that he had already been accused of not paying properly for his residence but “he gave all the necessary explanations — I am at his side”.
For his part, Cahuzac, a wealthy former plastic surgeon, continued to deny having a foreign account and said he planned to sue Médiapart.