Nomura Holdings was excluded as lead manager for several yen bond deals after authorities found market rule violations, the second time this year that Japanese companies cut underwriters over breaches.

At least four Japanese firms, including Toyota Finance, Sumitomo Mitsui Trust Holdings and Okinawa Development Finance, removed the nation’s biggest brokerage as bond manager after the development, according to underwriter announcements. Japan’s securities watchdog said it had investigated Nomura for suspected market manipulation in government bond futures and found violations.

Nomura’s shares tumbled as much as 7.9% Monday morning amid a broad selloff in Japanese stocks, with the Topix index dropping as much as 3.8%. Shigeru Ishiba’s victory at the ruling Liberal Democratic Party leadership contest wrong-footed investors who had bet on a boost from more monetary stimulus from his rival.

Regulatory troubles have prompted Japanese companies to remove brokerages from debt underwriting mandates in the past. Almost no Japanese company hired Mitsubishi UFJ Morgan Stanley Securities for several months for yen bond deals after regulators punished it over breaching information firewalls earlier this year, Bloomberg-compiled data shows.

Nomura’s removal as underwriter comes at a busy time for yen corporate bond deals. Sales of such notes have already reached a record in the fiscal first half started April, exceeding ¥10 trillion ($70 billion). The coming months are typically a busy time for brokerages in the yen primary market.

Hokkaido Electric Power dropped Nomura as a manager for yen transition bonds last week.