The U.S. Justice Department, Colorado, and nine other states have filed an amended lawsuit accusing six large landlords of conspiring to raise and keep rent high.

Several large landlords allegedly colluded in an effort to keep apartment rents high, including by using an algorithm that influences prices, according to new legal filings by the Colorado attorney general, the U.S. Justice Department and a coalition of other states.

Greystar, the largest U.S. apartment owner, and Blackstone’s LivCor are among the firms added to the suit.

The large landlords allegedly coordinated to keep Americans’ rents high by using both an algorithm to help set rents and privately sharing sensitive information with their competitors to boost profits.