WASHINGTON (Reuters) - Nine states, including Michigan and Nebraska, have joined a U.S. Department of Justice lawsuit against Alphabet's (GOOGL.O) Google which alleges the search and advertising company broke antitrust law in running its digital advertising business, the department said on Monday.

The states joining the lawsuit were Arizona, Illinois, Michigan, Minnesota, Nebraska, New Hampshire, North Carolina, Washington and West Virginia, the department said.

The government, which filed the ad tech lawsuit in January along with eight states, had argued that Google should be forced to sell its ad manager suite because it illegally abused its dominance of online advertising. Google has denied any wrongdoing and has asked Judge Leonie Brinkema in the Eastern District of Virginia to dismiss the lawsuit.

The Justice Department's ad tech lawsuit followed a separate lawsuit filed in 2020, at the end of the Trump administration, that accused Google of violating antitrust law to maintain its dominance in search. That case goes to trial in September.

The administration of President Joe Biden has sought to toughen antitrust enforcement. Alongside the Google lawsuit, it is also challenging multiple proposed mergers.