Brazilian prosecutors have charged Joseph Safra, the world’s richest banker, in connection with an alleged scheme to pay bribes to government officials in return for waiving tax debts.

The 77-year-old owner of Grupo Safra SA had knowledge of a 2014 plan by executives at his bank to pay $4.2 million in bribes to federal tax auditors, prosecutors said in a statement on Thursday.

The accusation is based on tapped phone calls between Banco Safra executive João Inácio Puga and tax officials, the statement added.

Safra, who alongside his family owns Banco Safra and a number of private-banking institutions, including Switzerland’s J Safra Sarasin, was not directly involved in the negotiations on the bribery plan, the statement noted. Still, the conversations showed that Puga informed Safra about the bribery talks, prosecutors said.

The bank denied the allegations, calling them “unfounded.”

There “have not been any improprieties by any of the businesses of The Safra Group,” it said in a statement.

No Safra Group representative “offered any inducement to any public official and the Group did not receive any benefit in the judgment of the tribunal,” the Safra Group statement added.

The charges filed are a follow-up of a broader police inquiry, known as “Operation Zealots,” into kickbacks by companies through lobbyists. Dozens of other Brazilian firms, including steelmaker Gerdau SA, have also been under investigation for suspected kickbacks.

The case is investigating whether companies bribed members of CARF, a body within the Finance Ministry, that hears appeals on tax disputes, to get favorable rulings that reduced or waived the amounts owed.

Over 70 industrial, agricultural, civil engineering and financial companies, including banks, are being probed in Operation Zealots.

Safra, a Lebanese-Brazilian billionaire, whose fortune is estimated at $13.4 billion by Bloomberg, controls a banking and financial conglomerate that operates in 19 countries.

In addition to Operation Zealots, Brazil has been gripped by the far-reaching corruption probe around state-run oil company Petroleo Brasileiro, known as Petrobras, and major engineering conglomerates in the past couple of years.