A software engineer laid off from Twitter last week complained to the National Labor Relations Board on Monday that he was illegally terminated after developing a web tool to help fellow employees preserve their work emails. In his filing, Emmanuel Cornet claimed Twitter had fired him in “retaliation for concerted protected activity” on Nov. 1, the same day he’d engaged in the supposed protected activity—sharing an email-saving Google Chrome extension he’d just published on a company Slack channel. The extension, according to Cornet’s complaint, “does something that anybody can do manually without it.” But ahead of mogul Elon Musk’s acquisition of the company, the tool was designed to aid workers concerned about layoffs and possibly losing access to important records, “such as statements reflecting their stock in Twitter, performance reviews, and other human resource documents.” After Cornet was fired, company officials removed his link from the Slack channel, he claims. Twitter, at Musk’s direction, began the process of firing about half its 7,500-strong workforce earlier this month, although Bloomberg News reported on Sunday that some have since been asked to return.