India could lose a vital U.S. trade concession, under which it enjoys zero tariffs on $5.6 billion of exports to the United States, amid a widening dispute over its trade and investment policies, people with close knowledge of the matter said. A move to withdraw the Generalised System of Preferences (GSP) from India, the world’s largest beneficiary of a scheme that has been in force since the 1970s, would be the strongest punitive action since President Donald Trump took office in 2017 vowing to reduce the U.S. deficit with large economies.