Dec 31 (Reuters) - A U.S. judge on Tuesday struck down a Florida law requiring drug screening for welfare recipients, saying that it violated the constitutional protection against unreasonable searches.

Florida Governor Rick Scott, a Republican who campaigned on a promise to expand drug testing, said he would appeal the ruling.

The law took effect in July 2011 and required parents to undergo and pay for urine tests for illegal drugs when they applied for Temporary Assistance for Needy Families, a federal-state program that helps poor people with children pay for food, shelter and necessities.

The testing fee of $25 to $45 was to be repaid by the state if the test came back negative, but applicants who tested positive would have been barred from receiving benefits for a year.

Enforcement of the law was temporarily halted in October 2011 after the American Civil Liberties Union sued, arguing that mandatory testing of people who were not suspected of using drugs violated the constitutional prohibition against unreasonable searches and seizures.

U.S. District Judge Mary Scriven permanently halted enforcement of the law in Tuesday's ruling. She agreed with an earlier court finding that "there is nothing inherent in the condition of being impoverished that supports the conclusion that there is a concrete danger that impoverished individuals are prone to drug use...."

The lawsuit was filed in U.S. District Court in Orlando on behalf of Luis Lebron, a U.S. Navy veteran, college student and single father with sole custody of his then-5-year-old son.

Lebron was denied benefits when he refused to take the test.

"The new law assumes that everyone who needs a little help has a drug problem," Lebron said when the suit was filed in 2011. "It's wrong and unfair. It judges a whole group of people on their temporary economic situation."

Scott and other supporters of the law argued that welfare recipients needed to be drug-free to prepare them for jobs. They said businesses had been requiring such tests for years and that government should do the same to ensure that taxpayer money wasn't used to buy illegal drugs.

"Any illegal drug use in a family is harmful and even abusive to a child," Scott said on Tuesday. "We should have a zero tolerance policy for illegal drug use in families - especially those families who struggle to make ends meet and need welfare assistance to provide for their children."

During the time the law was in effect, about 2.6 percent of recipients tested positive for illegal drugs, mostly for marijuana, according to the court documents.

The failure rate was well below that of the general population. The U.S. Department of Health and Human Services found in a 2009 survey that about 8.7 percent of the population aged 12 or older had used illicit drugs in the previous month.

Generally, the courts have allowed suspicionless drug testing only when public safety is at risk, such as for armed officers or railroad workers who operate heavy equipment.

The case is 6:11-CV-01473-MSS-DAB. (Reporting by Jane Sutton; editing by Gunna Dickson)