Japan's four opposition parties called on Bank of Japan governor Toshihiko Fukui to resign on Saturday over what many see as ethical lapses concerning his personal investments.
Fukui's judgement has been called into question since he revealed he invested 10 million yen ($85,820) seven years ago in a fund run by financier Yoshiaki Murakami, who was indicted on Friday for insider trading.
"Governor Fukui should be aware of his responsibility to revive internal and external confidence in the Bank of Japan and resign immediately," said a joint statement issued by the main opposition Democratic party and three smaller opposition parties.
The government has backed Fukui - seen as one of the most able central bank chiefs Japan has had in years - and Prime Minister Junichiro Koizumi said on Thursday Fukui had done a great job since he became governor.
The furore comes at a delicate time, as the BOJ considers implementing its first interest rate rise in six years, but Fukui has insisted that his troubles would not affect monetary policy decisions.
Fukui, who has repeatedly apologised for his actions, but declined to step down, is in Switzerland for a weekend meeting of the Bank for International Settlements.