Another group of Japanese investors has sued Mitsubishi UFJ Financial Group¡¯s joint brokerage venture with Morgan Stanley in the latest litigation over losses on Credit Suisse¡¯s riskiest debt, which became worthless.

A suit representing 26 plaintiffs seeking to recover losses from so-called Additional Tier 1 (AT1) notes sold to them by Mitsubishi UFJ Morgan Stanley Securities was submitted to the Tokyo District Court on Tuesday. The plaintiffs are seeking a combined ?1.73 billion ($12.2 million) in compensation according to the filing, which is led by Yamazaki Marunouchi Law Office.

A representative of the company, jointly owned by Japan¡¯s largest lender and the major U.S. investment bank, wasn¡¯t immediately available for comment. Two of the plaintiffs are companies, according to the complaint.

The move followed a separate ?5.2 billion suit filed earlier this year by the same law firm against the company on behalf of 66 different plaintiffs.

Mitsubishi UFJ Morgan Stanley Securities sold the securities more aggressively than any other firm in Japan, with its sales making up about two-thirds of the notes taken up, which totaled ?140 billion in value.

Global bondholders lost everything when Switzerland¡¯s regulator wrote down about $17 billion of Credit Suisse¡¯s AT1 notes during the firm¡¯s rescue by UBS Group, sparking lawsuits around the world. Investors in Japan have also sued the brokerage arms of SBI Holdings, Rakuten Group and Monex Group.

¡°It is uncommon in Japan for this many adversely impacted investors to file a group action against their brokerage,¡± said Matthew J. Wilson, president and dean of Temple University, Japan Campus. ¡°At the same time, it is equally uncommon for Japanese investors to lose their entire investment in a product due to the actions of a foreign government.¡±

The crux of the debate in Tokyo hinges around whether sellers met know-your-customer rules as well as adequately explaining to buyers the risks associated with the debt, including so-called viability events that would trigger a write-down.

The latest group of plaintiffs allege that Mitsubishi UFJ Morgan Stanley Securities violated a suitability principle, by selling the bonds to regular investors even though the products were intended for professional institutions.

Also, while the firm mentioned the write-down clause in a brochure, it fell short of offering the extra explanations needed for such investors to assess what could constitute viability events, according to the complaint.

Shinjiro Yamamoto, Mitsubishi UFJ Morgan Stanley Securities managing executive officer, said earlier this year that the brokerage had ¡°mostly done our work properly¡± in handling the sales.