Conservatives are starting to push the idea that city and county governments can pass union-restricting right-to-work laws, even though it may not be legal and has been tried only a handful of times in the last 70 years.

Right-to-work laws prohibit union contracts that require all employees to join the union, or at least pay union fees. Twenty-four states currently have versions of the law, which generally weaken unions by making it harder to sign up and retain members.

The common understanding is that federal law allows only states to enact the measures. But at a * Heritage Foundation forum Thursday, conservative labor policy experts said nothing explicitly prevents cities and counties from passing right-to-work ordinances too.

Heritage Foundation legal scholar Andrew Kloster said the issue is simply not mentioned in the 1947 Taft-Hartley law that allowed states to pass right-to-work laws. Most have assumed that Congress meant that only states had that right. Kloster argued otherwise.

"I personally don't think that is the case. It is certainly not clear. And that is the important thing: When it is not clear, the tie goes to the jurisdiction trying to pass their own law," Kloster said.

The American Legislative Exchange Council, which advocates that state and local governments adopt conservative legislation, already has a model of right-to-work legislation for states. The group is creating a "template" for local governments, too, said Jon Russell, director of the American City Council Exchange, a project of ALEC.

"In working with local officials across the country, I have come to realize that many of them don't fully understand how much leeway they actually have in decision-making such as [right to work]," Russell said.

However, they conceded that there is little legal evidence supporting their argument. That's because hardly anyone at the local level has ever thought to do it. There is virtually no case law on the subject.

A study Kloster wrote with fellow Heritage Foundation scholar James Sherk released Thursday could find only two federal cases since Taft-Hartley where the issue even came up.

In one, the court ruled the local ordinance was pre-empted by Taft-Hartley. The other, which involved Indian tribal land, said it wasn't pre-empted so it could be enacted.

"It is an open question. It has not reached the appellate courts or the Supreme Court," said National Right to Work Legal Defense Foundation lawyer William Messenger. "The locality would at the very least have a viable argument to fight back against the inevitable lawsuits."