One after another, major U.S. corporations have updated anti-discrimination policies to protect gay, lesbian and transgender workers, drawing plaudits from gay-rights groups. There's one prominent exception: Exxon Mobil. In the latest rankings of such corporate policies by the Human Rights Campaign, a national gay-rights group, many of Exxon's Fortune 500 counterparts got scores of 80 or higher on a scale of 100. Exxon, the nation's largest oil and gas company, became the first firm to get a score below zero. On Wednesday, in the latest attempt to pressure the company into change, a gay-rights group called Freedom to Work teamed with a high-powered Washington law firm to file what they described as a groundbreaking discrimination complaint against Exxon in Illinois.