Carla Gatza, the head of human resources for YogaWorks, said in an email that management respects the right of teachers and trainers to “engage in, or refrain from, union organizing” but “believes that our company, our employees, and our students are best served when YogaWorks and its employees work together without the interference of a third party union.”

Yoga has traditionally sought to unite the mind, body and spirit in an effort to achieve a feeling of serenity and a connection to oneself and the world. But over the past decade or so, many teachers say, studios have become increasingly commercialized.

YogaWorks, which began as a single studio in Southern California in the 1980s and is now one of the largest yoga chains in the country with around 60 locations, is seen by some teachers as emblematic of that shift.

In certain ways teaching yoga may seem like a dream job — a way to earn money while staying healthy and helping others. But yoga teachers say that their work can be filled with the type of stress that the practice is meant to alleviate.

Many, experts say, are participants in the so-called gig economy, where companies employ nonpermanent workers and don’t have to contribute to unemployment insurance or workers’ compensation, or heed minimum-wage and overtime laws.

Most YogaWorks teachers are something of a hybrid, classified as employees but given only part-time work with little or no job security, organizers said. And many of those teachers also do “gig work” as independent contractors for other employers. The effect, multiple instructors said, can be exhausting, with teachers constantly scrambling to make ends meet, competing for work and spending unpaid hours preparing for sessions.

Still, several teachers said, they stick with their classes because they enjoy their jobs and they believe in the ability of yoga to improve lives.