For many students, the class is as much about the spirit as it is about exercise. But for the Missouri Department of Revenue, it's strictly recreation, and the state recently informed yogis that starting this month, studio owners and instructors must charge a 4 percent sales tax on class fees. The tax has roiled the normally serene yoga world, whose supporters maintain their pastime should be exempt from sales tax as a spiritual pursuit. 'Is this only stretching? No,' said Karen Jones, who opened the Marbles studio in 2003. 'I think this is just another way for the state to get money.' Many yoga practitioners say they are confused as to how their ancient practice that merges physical and mental disciplines with meditation could possibly be equated with aerobic pole dancing or Tae Bo workouts. But the state -- one of the few in the country to tax yoga instruction -- argues that it is not infringing on religious practices and only levying a legitimate tax on businesses. Ted Farnen, a spokesman for the Department of Revenue, pointed out that gyms and fitness centers that offered yoga classes already had been remitting the sales taxes for years, as had some yoga centers. 'It's one thing if you're going into a temple and doing yoga,' Farnen said. 'It's another if you're going to a studio and paying a fee to do yoga.' Most services, such as yoga classes or swimming pool lessons, are generally not charged sales tax around the country. Some states, however, have provisions that allow them to tax certain categories of services. In Missouri's case, some areas where sales tax can be applied include amusement, entertainment and recreation services, which includes such disparate items as football tickets, gym memberships and concert admission. Yoga managed to fly under the state's regulatory radar until a 2008 state Supreme Court decision, which ruled that fees people pay for personal training services at a gym are taxable. When the Department of Revenue's attorneys were reviewing the case this fall, they determined that yoga and Pilates centers offered similar type of training services. That made them places of fitness and recreation, they decided, not worship. The Department of Revenue sent out letters informing 140 yoga and Pilates centers that they should be registered with the state and start remitting sales tax as of Nov. 1. 'We only sent letters to those that charge for their yoga or Pilates services, not to temples or other religious centers that offer yoga as part of their religious framework,' Farnen said. The effect was quickly felt. Stacy Broussard, a yoga instructor who teaches at Urban Breath studio in St. Louis, said the sales tax had already begun to eat into her revenue. 'Money's already tight for people and since this went into effect in November, I'm hearing more and more people say they're hesitant to buy blocks of classes,' Broussard said. 'They're coming in less frequently to class.' Yoga supporters have mobilized to fight back. Students banded together, along with instructors and studio owners affiliated with the Spirit of Yoga St. Louis, to protest the tax. 'Yoga is a spiritual practice. It's not a purchase,' said studio owner Bruce Roger, a St. Louis resident who has been an instructor for 25 years. 'Somehow, we need to get the state to realize that.' Jones glanced across her studio floor, where a dozen men and women in loose-fitting shirts and cotton pants sat barefoot and cross-legged on the wood floor. Flute music played softly in the background, as the group meditated. Some quietly chanted, as an instructor encouraged the students to focus on 'movements that connect earth to heart.' 'Why would you call what we do entertainment and recreation?' Jones asked. Yoga supporters successfully have argued their case in Connecticut and Washington state. When Washington started requiring studios to charge sale tax for their classes last year, studio owners and teachers met with lawmakers and regulators to talk about how people used yoga to achieve spiritual enlightenment. The department of revenue reversed its decision, and yoga centers are now exempt. 'After we talked, we realized they had a point,' said Mike Gowrylow, a spokesman for the Washington Department of Revenue. But it's easy to see why regulators, unfamiliar with yoga, may only be seeing how big the business has become. Last year, Yoga Journal estimated that the field had grown into a $6 billion industry in the United States. A number of states have tried to regulate yoga instructor programs. These states say yoga schools should have similar fees as other vocational training outlets, such as dance studios or dog grooming salons. Earlier this month, three yoga instructors in Virginia filed suit in federal court to stop the state's plan to start regulating yoga schools. The teachers claim that to teach yoga is to pass on an ancient tradition, and therefore the state's plan is a violation of their First Amendment rights. State officials have argued that they are trying to protect students, who can spend thousands of dollars getting the training to land a job or teach yoga. (Optional add end) There are an estimated 1,000 schools that train instructors, according to the nonprofit Yoga Alliance, which was launched to help encourage self-regulation in the industry. 'As yoga has grown in popularity, it's become more visible and garnered the attention of regulators,' said R. Mark Davis, president and chief executive of the Arlington, Va.-based alliance. Even practitioners are not uniform in their view of yoga's spiritual side. 'The studio I teach at doesn't say yoga is spiritual because it could turn off a ton of potential customers,' said Ellen Stansell, an adjunct humanities professor who teaches courses on the history and philosophy of yoga at the University of Houston, in Victoria, Texas. 'But we do hold that space open for students to bring their spirituality into the studio, if they want to,' she added. 