Jun Tada, an aide to indicted House of Representatives lawmaker Muneo Suzuki, concealed 90 million yen in income for seven years through 2001, sources said Thursday.
The Tokyo Regional Taxation Bureau found that Tada, 51, who has also been indicted in connection with Suzuki's bribery scandals, did not declare funds he had personally received from Suzuki supporters during those years, the sources said.
Tada has since revised his tax statements and paid more than 30 million yen in arrears and penalties, they said.
According to the sources, it was Tada who dealt with firms supporting Suzuki at the lawmaker's office near the Diet when they visited to donate funds.
Tada received several hundred thousand yen from them per visit as rewards for his services, according to the sources.
The tax authorities found that much of the cash Tada received was deposited into the account of an acquaintance and into other accounts, and that Tada did not declare the money as income, the sources said.
They said investigators uncovered the undeclared donations from Suzuki supporters to Tada while they were looking into the lawmaker's alleged misdeeds.
Prosecutors then alerted the Tokyo tax bureau about Tada's questionable tax practices.
Suzuki, 54, faces two charges of taking bribes amounting to 11 million yen from two Hokkaido companies, as well as charges of perjury and falsifying political funds reports in 1998.
He quit the ruling Liberal Democratic Party but has rejected calls to resign as a lawmaker.
Tada, the government-paid policy secretary to Suzuki, faces the same charges as his boss, except for the count of perjury.
Both are undergoing criminal trials and have pleaded not guilty.