The three major networks, CNN, Fox News and The Associated Press filed a lawsuit Monday asking a federal judge to strike down a South Dakota law that prevents exit polling within 100 feet of a voting place.

The law violates the First Amendment because it restricts the news organizations' speech and commentary about the political process and limits their opportunities to gather information about that process, according to the lawsuit.

The lawsuit, filed in federal court in Sioux Falls, asks that the case be handled quickly because South Dakota's primary election is June 3, just three weeks away. It seeks a preliminary ruling before the primary to prevent South Dakota officials from barring exit polling within 100 feet of polling places.

The lawsuit was filed by ABC, CBS, NBC, Cable News Network, Fox News Network and the AP.

Poll representatives working for the news organizations have conducted exit polling within 100 feet of South Dakota voting locations in past elections, according to the lawsuit.

However, South Dakota Secretary of State Chris Nelson told polling representatives in an April 2 e-mail that exit polling would only be allowed within the bounds of the state law that bars exit polling within 100 feet of a polling place, the lawsuit said. Nelson warned in the e-mail that a violation of the law "will be dealt with by all legal means including prosecution."

The accuracy and reliability will be harmed because exit pollers may not be able to question some voters, the lawsuit asserts. Some voters may get into cars and leave before exit pollers can ask if they want to fill out questionnaires, hurting the accuracy of the polls, it says.

Nelson said Monday he had not had time to study the lawsuit in detail. But he said the purpose of the exit-polling law is to maintain the integrity of the polling place. "We certainly feel that's an important principle to uphold."

He said exit polling has not been a problem in past elections because the law has always required it to be done outside the 100-foot area around a polling place.

"So when it's done outside of that 100-foot area, it doesn't interfere with people's coming into the polling place or coming out of the polling place or subject the voters to the questions of exit pollers when they may be in the process of voting," Nelson said.

Exit polls provide information valuable to news organizations and scholars because they help analyze voting patterns according to gender, age, income, race, religion and other categories, according to the lawsuit. The information helps explain how and why people voted for or against particular candidates.

Copyright 2008 Associated Press