The Justice Department has expanded a lawsuit against the real estate software company RealPage, adding six of the biggest landlords and property management companies in the country to the suit and alleging that they coordinated to keep rents artificially high.

An amended complaint names six landlords as defendants in ongoing litigation that North Carolina and several other states, along with the federal government, began in August.

After suing real estate software company RealPage in late August, the U.S. Department of Justice (DOJ) expanded its lawsuit on Wednesday to include six major landlords. According to the DOJ, the landlords worked with RealPage to keep rent prices high by sharing sensitive information.

Federal prosecutors sued the real estate software company RealPage in August, now they're suing some of the company's biggest customers.

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The Justice Department is adding six major apartment landlords to its lawsuit against real-estate software company RealPage, expanding the scope of its allegations that the rent-setting algorithm enabled illegal price fixing.

Greystar, Blackstone, Camden Property Trust and Cushman & Wakefield are among the firms added to the suit that alleges RealPage enabled landlords to fix rents.

The U.S. Department of Justice has accused several Houston-area landlords of colluding to inflate rent prices, expanding its antitrust case against RealPage, a Texas-based company whose software at the center of an alleged rent price-fixing effort.

The Department of Justice alleges several property management companies colluded to inflate rents using algorithmic software, harming millions of renters in Houston and across the country.