Yoga teachers in Missouri say they should be exempt from the state sales tax because their students learn a spiritual discipline, not just a physical one.

The 4 percent tax, also imposed on other types of spectator and participatory sport from Cardinals' games to health clubs, was extended to yoga studios Sunday, the St. Louis Post-Dispatch reported Tuesday.

Missouri is the only state at the moment that taxes yoga. Washington state dropped a yoga tax last year after a massive lobbying effort by practitioners.

David Zanone, manager of the Missouri Department of Revenue taxation division, notified 140 yoga and Pilates studios Oct. 13 they were subject to state sales tax.

Missouri simply did not try to collect taxes from yoga studios for years, although even yoga teachers concede that many U.S. practitioners do it as a physical discipline.

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