The law was first introduced four years ago, with about 57 percent of voters supporting the referendum, the New York Times reported Wednesday.
In a special election Tuesday, even more voters supported keeping the law, with 60 percent voting in favor of it, unofficial election results from the Dodge County Election Commissioner indicated.
The law prohibits landlords from renting to illegal immigrants and requires renters to apply for a permit to declare they're in the country illegally, the Times reported.
The American Civil Liberties Union criticized the measure and said it planned to keep a watchful eye out for discrimination as the measure is enforced.
"We are saddened by the result of today's vote, and will stand with those residents of Fremont who will be harmed by the unfortunate decision to allow a discriminatory housing ordinance to be implemented," the group said in a statement.