WASHINGTON — The Justice Department said it will require the biggest voting machine company in the country to sell off key assets following a merger that left the firm in control of more than 70 percent of U.S. voting equipment systems. The federal government and nine state attorneys general filed a lawsuit Monday saying the combination last September of Election Systems & Software and its biggest competitor harms competition.

Under a proposed settlement, ES&S would sell voting equipment system assets it bought from Premier Elections Solutions, a subsidiary of Diebold. The proposed settlement, to which both sides have agreed, must be approved by a federal judge before it becomes final.

The assets include the means to produce all versions of Premier's hardware and software that record, tabulate, transmit or report votes.

Before the merger, ES&S, based in Omaha, Neb., had systems installed in 41 states.