For people not reading the article, Twitter was facing a class action lawsuit, but they successfully sued to force employees to go through arbitration, which avoids a class action suit. Only problem is that arbitration rules say the employee has to pay a small fee for filing, but the company has to pay the arbitration costs. Twitter filed to force the costs to be split with the employee, but the organization that overseas arbitration said that's against their rules and has refused to engage in any arbitration activities that Twitter isn't paying for. The pricetag could be millions, and Twitter is simply not paying, so now the employees are suing to force Twitter to pay.