The Justice Department on Tuesday sued Google for antitrust violations, alleging that it abused its dominance in online search and advertising to stifle competition and harm consumers. The lawsuit marks the government's most significant act to protect competition since its groundbreaking case against Microsoft more than 20 years ago. Eleanor Fox, a professor of law at New York University School of Law says the charges will be very hard to prove. Lawmakers and consumer advocates have long accused Google, whose corporate parent Alphabet Inc. has a market value just over $1 trillion, of abusing its dominance in online search and advertising to stifle competition and boost its profits. Critics contend that multibillion-dollar fines and mandated changes in Google's practices imposed by European regulators in recent years weren't severe enough and that structural changes are needed for Google to change its conduct. "I think this is not an effective deterrent money wise, so that's why some people say you've got to break them up because they have bad incentives, " Fox said. The Justice Department isn't seeking specific changes in Google's structure or other remedies at this point, but isn't ruling out seeking additional relief, officials said. The case was filed in federal court in Washington, D.C. It alleges that Google uses billions of dollars collected from advertisers to pay phone manufacturers to ensure Google is the default search engine on browsers. Eleven states, all with Republican attorneys general, joined the federal government in the lawsuit. President Donald Trump's administration has long had Google in its sights. One of Trump's top economic advisers said two years ago that the White House was considering whether Google searches should be subject to government regulation. Google controls the vast majority of global web searches. The company has been bracing for the government's action and is expected to fiercely oppose any attempt to force it to spin off its services into separate businesses.