Tour operators Bill Main and Tonia Edwards understand the city's need to regulate certain aspects of their Segway sightseeing tours to make sure, for example, that clumsy tourists don't become two-wheeled gyroscopic menaces on city sidewalks.

What they can't abide, though, are regulations to ensure all tour guides are knowledgeable on the city's history and architecture, among other things. They say the city has no business issuing licenses to permit some and deny others the right to describe people and places in the city.

On Thursday, Main and Edwards, who own the Segs in the City tour company, sued the city in federal court and asked a judge to invalidate the city's new regulations on free-speech grounds.

Main, a Baltimore resident who came to the United States from Australia in the 1990s, said he follows regulations that require his Segway tourists to travel at safe speeds and keep off sidewalks in certain parts of the city.

"But when they pass regulations on what we are allowed to say, we take exception," Main said.

A spokesman for the city's Department of Consumer and Regulatory Affairs said the city has had regulations for tour guides for years.

"The District of Columbia licenses all businesses to give consumers a level of comfort about the product or service they are paying for," said Mike Rupert, a spokesman for the city's Department of Consumer and Regulatory Affairs.

Some tour guides say the new regulations ensure that tourists are well served when they visit Washington. Jim Heegeman, president of the Professional tour Guides of Washington D.C., said it's a good thing that the city ensures tour guides have at least rudimentary knowledge of the city's history. A big chunk of tour guides' business is schoolchildren visiting Washington on field trips, he said, and they would be ill-served by an uninformed tour guide.

But lawyer Robert McNamara says any regulatory scheme that attempts to license tour-guide operators will be unconstitutional because it gives some people a right to talk about the city and denies it to others. The regulations, he said, punish people for what amounts to "unauthorized talking" by up to 90 days in jail.

McNamara, a lawyer with the Institute for Justice, an Arlington, Va.-based legal group that is representing Main and Edwards, said there has been a proliferation of occupational licensing regimes in recent years. The institute challenged similar regulations on tour guides in Philadelphia; the case is on appeal after a judge dismissed the case because the city has not yet tried to enforce its regulations.

Last year, the institute sued to prevent the state from regulating yoga teacher-training programs; the state's General assembly passed legislation in response that exempts the yoga teachers from certification.

And the institute won a U.S. Supreme Court case on behalf of a Virginia vintner who challenged regulations that barred her from shipping wine to out-of-state customers.

Ultimately, McNamara said, the institute is hoping the U.S. Supreme Court will take a case that will definitively state the circumstances under which state and local governments can require occupational licenses.

The city has actually had regulations in place for many years to license tour-guide operators, but they were so unwieldy that the city has not enforced them, McNamara said. The old regulations require tour-guide operators to be city residents and submit certification from a physician that the applicant is not a drunkard.

The test on the city history and buildings was part of the old regulatory scheme and remains in the new regulations, which took effect in July.