Credit Suisse bondholders have launched a legal challenge in Switzerland against regulators’ decision to write down $17bn in securities as part of UBS’s rescue of the troubled bank last month.

Bondholders holding about $5bn of Credit Suisse’s cancelled debt want the decision to write down their bonds revoked or amended, according to an outline of their appeal made in a Swiss administrative court and reviewed by The Wall Street Journal. The bondholders are alleging the total write-down was disproportionately punitive to them and violated their property rights, according to the summary of the legal filing.