The Upper House passed a resolution Wednesday to punish member Antonio Inoki for visiting North Korea without the chamber's permission, the first such disciplinary action in more than 60 years.
A panel will decide on the precise punishment as early as this month, according to lawmakers.
"I accept it seriously," Inoki told reporters following the vote by the Upper House plenary session.
The parties from both the ruling and opposition camps that backed the motion said his act breached parliamentary rules and disrupted the chamber's order.
The most severe punishment the disciplinary panel can impose would be kicking Inoki out of the Diet. Whatever it decides will be subject to another vote by the full Upper House.
Japan has no diplomatic relations with North Korea and bilateral ties have long been icy over issues such as Pyongyang's abductions of Japanese citizens in the 1970s and '80s. Lawmakers are required to obtain permission from the Diet to visit the country.
Inoki, a member of the opposition Nippon Ishin no Kai (Japan Restoration Party), visited North Korea for six days through Nov. 7, during which he met with some senior officials, including an uncle and top aide to leader Kim Jong Un.
The main purpose of the visit, however, was widely seen as promoting sports exchanges. Inoki, a former pro wrestler, opened an office in Pyongyang for his nonprofit group for that purpose.
Inoki, 70, whose real first name is Kanji, was already known for his repeated visits to North Korea before he became a lawmaker in July's Upper House election.
His party decided Tuesday to suspend his membership for 50 days for making the unauthorized trip. On Wednesday, the party voted against the disciplinary motion in the Upper House.
