The undercount could affect the outcome of the District 13 U.S. House race, where Democrat Christine Jennings is behind her Republican opponent, Vern Buchanan, by just 368 votes. The District 13 seat is now held by Katherine Harris, the controversial former secretary of state of Florida who fell short in her bid to unseat incumbent Democratic Sen. Bill Nelson.

There have been in recent days that voters had difficulties with the county's iVotronic touch-screen systems, and concerns that the e-voting hardware didn't record votes for the congressional race.

The machines are made by Election Systems & Software Inc. (ES&S) in Omaha.

Jennings posted a statement on her saying that there would be a mandatory recount because of the slim margin separating the candidates. "The supervisor of elections reported Friday that there were 18,382 under-votes in this congressional race -- that means more than one out of every seven ballots cast did not record a vote for the 13 District Congressional race," Jennings said in the statement. "This is a staggering number. Sarasota voters have been victimized by not having their vote count."