The Digital Markets Act is the most sweeping piece of digital policy since the EU put the world's toughest rules to protect people's online data into effect in 2018. The legislation is aimed at stopping the largest tech platforms from using their interlocking services and resources to box in users and squash emerging rivals. Violators of the law, which will take effect as early as later this year, could face penalties of up to 20 percent of their global revenue.