WASHINGTON  Democrats are charging that commercials financed by an increasingly prominent conservative foundation with ties to the Tea Party violate the foundation’s tax-exempt status.

In a complaint filed this week with the Internal Revenue Service, lawyers for the Democratic Congressional Campaign Committee charged that the group, the Americans for Prosperity Foundation, has been running advertisements in Kansas, Missouri and Michigan that are inherently “political in nature,” contravening a ban under federal tax law. A copy of the complaint was provided to The New York Times.

The foundation, which has just begun a $1.4 million ad campaign criticizing the economic policies in Washington as “wasteful spending,” has become a vocal critic of Democratic policies and drew a rebuke this month from President Obama.

Nonprofit groups like the foundation, which falls under section 501(c)3 of the tax code, are forbidden from participating in “any political campaign on behalf of or in opposition to a candidate.” They may, however, seek to educate voters or conduct broader get-out-the-vote drives “if conducted in a nonpartisan manner,” the I.R.S. says.