On Sunday, Missouri became the only state to enforce a sales tax on what many see as a spiritual pursuit — the practice of yoga.

The debate between Missouri's yoga community and the state centers on whether yoga is a spiritual practice or just exercise. If it's one, it's constitutionally protected and can't be taxed. If it's the other, Missouri's cash-strapped budget has a new source of revenue.

On Monday, yoga studio owners pledged to fight for their students and educate state legislators about yoga's spiritual roots.

Last year, a similar First Amendment battle broke out in Washington when that state began including yoga studios in a group of recreational organizations that had to charge customers a sales tax. Yoga practitioners, teachers and studio owners in Seattle and around the state came together to show legislators and the Department of Revenue that yoga was different from other physical activities.

"They told us that yoga is more than just staying physically fit; it's more of a spiritual and mental type of exercise," said Mike Gowrylow of the Washington Department of Revenue. "After they educated us, we agreed they had a point."

The state decided to leave yoga studios alone.

The Missouri yoga community and the state's Department of Revenue are now at similar cross-purposes. Like many states, Missouri leaders are looking to alternative sources of revenue as budgets continue to tighten. If the state prevails, it will be the only one in the country to levy sales taxes on the spiritual services provided by yoga studios.

"The Missouri Supreme Court has held that athletic and fitness clubs are places of recreation and therefore fees paid to these types of businesses are subject to sales tax," David Zanone, manager of the Missouri Department of Revenue's taxation division, wrote to 140 yoga and Pilates studio owners in a letter dated Oct. 13. "Yoga centers offer the same types of fitness services that the Missouri Supreme Court has held are taxable."

At issue is a Missouri statute that mandates a 4 percent tax on fees charged for athletic events like Cardinals games, fitness club memberships and other entertainment, amusement or recreation businesses.

Yoga teachers say the service they provide is not recreation, but a form of physical preparation for meditation, based on ancient Hindu texts, with the ultimate goal of spiritual enlightenment.

But even yogis concede the American interpretation of yoga that has blossomed, especially in the last 30 years or so, has become popular for its stress-reducing properties and physical health benefits.

There are dozens of different styles of yoga. Practitioners can be found both in traditional gyms, among free weights and elliptical machines, and in self-contained studios whose owners are more inclined to teach yoga's spiritual foundations.

That tension — yoga as meditation versus yoga as exercise — is at the heart of the argument that yoga teachers plan to make to legislators in Jefferson City in coming weeks.

For years, the state has simply not required yoga studios to charge a sales tax.

"A lot of studios felt safe because they were primarily offering yoga classes," said Lucy Holmes, who teaches yoga at a number of area studios. "But a lot of us thought this was a sleeping dog that might come back and try to bite us, and now it has."

In Washington last year, that state's Department of Revenue told several studios they owed "tens of thousands" in back taxes, according to Anne Phyfe Palmer, director of 8 Limbs Yoga Centers in Seattle, and a leader in the movement against the Washington tax. "That created much more of a push-back" from the yoga community, ultimately resulting in an organized effort to change the legislation.

Erin Stack, co-owner of Bikram Yoga St. Louis in Richmond Heights and Chesterfield, said her studio has been paying the tax since it opened in 2003. Even so, she calls the tax "ridiculous and unnecessary," and said she'd be joining the fight against it.

Mike Shabsin, an attorney at Sher & Shabsin who teaches yoga at Big Bend Yoga Center at Webster Groves, said he didn't know why Missouri had exempted yoga studios from the sales tax for so long, but his plan is to restore that exemption and to make it permanent.

"Washington and Connecticut have carved out exemptions for yoga, tai chi and qigong as spiritual practices, and centers that teach those techniques are excluded from sales taxes for that reason," Shabsin said. "Our hope is that Missouri will recognize the same thing."

In a statement, the Missouri Department of Revenue said the sales tax for yoga studios "has long been on the books" and "was recently clarified" by a 2008 Missouri Supreme Court case. The department, it said, is not seeking retroactive payments and "will consider religious exemption issues on a case-by-case basis."

Two weeks ago, yoga studio owners and teachers in the area gathered to discuss how to respond to the state's decision to begin collecting sales taxes on Nov. 1. The group, organized under the umbrella organization Spirit of Yoga St. Louis, decided to focus on education, including a Legislative Yoga Awareness Day, and meetings with state lawmakers.

Shabsin said the group will encourage legislators to come up with a definition for a "place of amusement, entertainment or recreation."

"We feel that yoga taught in a studio is actually instruction on an ancient spiritual practice, not an amusement, entertainment or recreation," he said.

For now, yoga studio owners said they would comply with the request to collect sales tax, even as they prepare to fight it. For a typical 90-minute session, a teacher might charge a student $15.60, instead of $15; the yoga studio would subtract 60 cents and send it to the state.

"Our studio will pay the sales tax under protest, so when we lobby the Legislature, we'll have a stronger voice," said Brigette Niedringhaus, owner of Southtown Yoga in St. Louis.

If the sales taxes are collected under protest and the studio owners later win a legal battle with the state, the studios will receive the returned sales taxes, not their customers.

"In the meantime, we'll educate people about what yoga really is, instead of just saying 'you don't understand us,'" Niedringhaus said. "That wouldn't be an especially yogic way of approaching it."