It seemed like a good idea at the time. Ten years ago, with yoga transforming into a ubiquitous pop culture phenomenon from a niche pursuit, yoga teachers banded together to create a voluntary online registry of schools meeting new standards for training instructors.

But that list  which now includes nearly 1,000 yoga schools nationwide, many of them tiny  is being put to a use for which it was never intended. It is the key document in a crackdown that pits free-spirited yogis against lumbering state governments, which, unlike those they are trying to regulate, are not always known for their flexibility.

Citing laws that govern vocational schools, like those for hairdressers and truck drivers, regulators have begun to require licenses for yoga schools that train instructors, with all the fees, inspections and paperwork that entails. While confrontations have played out differently in different states, threats of shutdowns and fines have, in some cases, been met with accusations of power grabs and religious infringement  disputes that seem far removed from the meditative world yoga calls to mind.

In April, New York State sent letters to about 80 schools warning them to suspend teacher training programs immediately or risk fines of up to $50,000. But yogis around the state joined in opposition, and the state has, for now, backed down.