A growing number of school districts and states are trying to give teachers random drug tests, citing student safety concerns, but their efforts are running afoul of unions who say such tests violate teacher privacy rights.

In Missouri, the House education committee is weighing a bill that would require districts to randomly test teachers for drug use. Hawaii last year adopted a policy allowing teachers to be randomly tested, but implementation was stalled after the teachers union sued to block the policy as unconstitutional.

Elsewhere, at least four districts that have tried to implement random testing are either facing or have faced court challenges, with teacher groups, unions and civil libertarians invoking the Fourth Amendment that guarantees protection against unreasonable searches and seizures.

Supporters say teachers need to be tested for drug use because of a safety issue: children spend most of their waking hours in the company of teachers.

Why should a school employee not be tested? After all, police officers, factory workers and people in most other industries can be randomly tested for drug use, said Missouri state Rep. Don Wells, a Republican who introduced the bill for testing teachers in his state's House.

The bill would require that districts randomly test teachers for narcotics in their bloodstream. Teachers who test positive would be fired.

Opponents of teacher drug testing say mandates such as ongoing, random tests are unnecessary, expensive and invasive.

Folks who go into teaching are not the kind who use drugs, said Michael Simpson, assistant general counsel for the National Education Association (NEA), the nation's largest teachers union with 3.2 million members.

He said the NEA supports testing of teachers when an administrator trained to detect drug abuse has reasonable suspicion that a teacher could be under the influence. Most districts now require such testing. But policies testing teachers for drugs at random force districts and states to spend precious education dollars, Mr. Simpson said.

In the Missouri bill, a fiscal note cites the cost of a single test at $51. Districts estimate that the cost could add up into thousands of dollars each year if they were to implement such testing.

Maryland, Virginia and the District have no policies requiring teachers to be tested randomly for drugs.

This issue hasn't popped up here in Maryland, said Dan Kauffman, spokesman for the Maryland State Teachers Association.

Virginia Department of Education spokeswoman Julie Grimes said such a policy has not come up for consideration by either the department or the state legislature. School districts in the greater D.C. area also say they have no such policies, nor are any under consideration.

In Fairfax County, spokesman Paul Regnier said the district would test any employee or student on suspicion of drug use. However, he said, the district has never considered a policy on randomly testing teachers for drugs.

We do a very careful background check including fingerprints and previous arrest records before hiring teachers, Mr. Regnier said.

Montgomery County Public Schools spokeswoman Kate Harrison said her district does not have a policy on random drug tests for teachers, nor does it have a policy requiring teachers suspected of drug use to be tested. However, she added, if there is any indication that the teacher is unfit, the administrator and human resource office could legally call for an investigation.

Hawaii's policy resulted from a push by Gov. Linda Lingle, a Republican, after six teachers were arrested in unrelated drug cases. The state Department of Education and the Hawaii State Teachers Association signed a contract last year agreeing to the tests in exchange for an 11 percent salary raise.

But when the state insisted that anyone in the state's 13,000-teacher work force could be tested at random under the policy, the teachers union, which said it had hoped to negotiate how the policy would be implemented, invoked teacher privacy rights and asked the state Labor Relations Board for a ruling. The board referred the matter to the circuit court, which has yet to issue a ruling.

Roger Takabayashi, the president of the Hawaii State Teachers Association, added that the union is prepared to go all the way to the state Supreme Court to ensure that teacher privacy rights are not violated.

Mitsue Kaneko, a special assistant in the Hawaii department of human resources, said that the testing was not meant to be punitive, but rather a deterrent. Teachers who tested positive would not be fired but would receive help recovering from drug abuse, she added.

Court rulings on the issue of testing teachers for drug use have gone both ways. While judges have sided with the teachers on privacy rights in some districts, others have agreed that districts can indeed test teachers.

In West Virginia, a federal judge in late December ruled against a new drug testing policy in the Kanawha County school system, saying it would force teachers to submit to an unconstitutional and unjustified search.

In Louisiana, the East Baton Rouge teachers union last year challenged a decade-long district policy for testing teachers who were injured on the job. The district, under a court injunction last month, agreed to suspend the testing for injured teachers. But it is continuing with a random drug testing policy under which it tests about 5 percent of the employees in the district in any given year, school district spokesman Chris Trahan said.

The American Civil Liberties Union of Louisiana joined the teachers union in challenging the policy.

It is a warrantless and suspicionless invasion of privacy, Louisiana ACLU Executive Director Marjorie Esman said. She noted that urine tests used to detect drugs reveal other private medical information, including prescription drugs that the teacher may be using, and even pregnancy.

But some districts in Kentucky and Tennessee have been randomly testing teachers for drug use for years, and some say the policy has helped. In Knott County, Ky., a federal court judge upheld testing teachers for drugs on the grounds that school officials had the authority to ensure a safe environment for children.

Knox County, Tenn., which won a lawsuit filed by its teachers union over its drug-testing policy, now tests all teachers before it hires them, but not after they have started working in the district. Kathy Sims, the executive director of human resources for Knox County Public Schools, said that the policy has been effective.

On average each year, she said, four or five hopeful employees test positive. It is a great safety device with the well-being and safety of our students at heart, she said.

But teachers who have had to go through drug tests say they are humiliating. In East Baton Rouge, teacher Peggy Reno filed a lawsuit against the district. She said she was asked to take a drug test after she injured her shoulder while trying to break up a fight between two students.

Her attorney, Yigal Bander, who also represented the local teachers union in its lawsuit against the policy, said that immediately after the attack, instead of being offered any comfort or medical attention, Ms. Reno was asked by administrators to report immediately for a drug test.

She was asked to wait around in a clinic for a drug test as if she was suspected of something, Mr. Bander said. But she was just doing her job, and there was no suspicion of drug or Alcohol use.