COLUMBUS, Ohio--A political watchdog organization is accusing a Dayton-based dark-money group of violating federal tax and campaign-finance law by undercounting the amount it spent on anti-Democrat attack ads.

Freedom Vote Inc., led by former Republican National Committee political director James Nathanson, failed to report more than $1.1 million worth of spending on ads opposing 2016 Democratic U.S. Senate nominee Ted Strickland, according to complaints filed Tuesday by the group Citizens for Responsibility and Ethics in Washington (CREW) with the IRS and Federal Election Commission.

Freedom Vote doesn't have to pay taxes, as it's registered as a social welfare group under section 501(c)(4) of the tax code. Under the law, a 501(c)(4) organization is allowed to engage in political activities so long as they're not the primary focus of the group.

Between October 2015 and September 2016, Freedom Vote reported political spending of more than $1.7 million - 48.8 percent of the group's overall spending, according to a CREW statement. But when the anti-Strickland ads are factored in, about 80 percent of Freedom Vote's spending during that time was political, the group asserted.

CREW, based in Washington, D.C., has asked the IRS to investigate whether Freedom Vote violated its tax-exempt status and requested that the FEC make the group register as a political committee (a step that would force Freedom Vote to disclose its donors).

Nathanson didn't return a phone call seeking comment Wednesday.