WASHINGTON — A campaign finance watchdog group on Friday filed a complaint with federal regulators against two groups — one pro-Republican and the other pro-Democrat — alleging they violated the law by airing political ads during the presidential contest.

Democracy 21 wants the Federal Election Commission to investigate the American Issues Project, which ran a $2.8 million ad campaign against Democratic presidential nominee Barack Obama, and the American Leadership Project, a group that backed Sen. Hillary Rodham Clinton in the Democratic primaries and ran about $4.3 million in ads supporting her or against Obama.

The complaint argues that both groups violated the law by not operating as a political action committee, which would have restricted their fundraising to capped donations. The American Leadership Project was largely financed by unions that supported Clinton. The American Issues Project ad against Obama was paid for by Texas billionaire Harold Simmons, a McCain fundraiser.

"The FEC complaint we filed today is intended to help ensure that the FEC continues to take enforcement action against any illegal activities by outside spending groups that may occur in the 2008 election," said Fred Wertheimer, the president of Democracy 21.

Neither group had an immediate response.

The American Issues Project is a nonprofit 501(c)4 organization. It ran ads in August in Michigan and Ohio linking Obama to William Ayers, a Vietnam-era militant who helped found the violent Weather Underground. Ayers, now a university professor in Chicago, has worked on charity and education projects with Obama and hosted a political meet-and-greet for Obama in the 1990s.

As a 501(c)4 organization, the group must have as its main purpose a mission other than seeking to influence elections. Wertheimer also wrote to the Internal Revenue Service asking the IRS to examine whether the group violated its nonprofit status.

The American Leadership Project was created as a 527 group, named after the section of the tax code that governs them. Its main contributors were the American Federation of State, county and Municipal Employees and the American Federation of Teachers. The group also ran a radio ad against McCain in Colorado against McCain during he Democratic National Convention.