The Plumbers and Steamfitters Local 137 Pension Fund are seeking class action status on behalf shareholders who suffered losses after American Express in February announced the end of its co-branding agreement with Costco Wholesale Corp.

AmEx at the time said the loss of the contract, set to expire March 31, 2016, would hurt earnings for the next two years.

Over the next two days, AmEx's stock plummeted, losing $8 per share to close at $77.53, according to the lawsuit. The decline wiped out close to $9 billion of market value.

More details here.