Are employers required to grant Muslim employees prayer breaks?

[Yo_Mama]

59. US law mandates reasonable accommodation.

https://www.eeoc.gov/laws/types/religion.cfm

However it does not provide that an employer must impair its basic business efficiency:

The law requires an employer or other covered entity to reasonably accommodate an employee's religious beliefs or practices, unless doing so would cause more than a minimal burden on the operations of the employer's business. This means an employer may be required to make reasonable adjustments to the work environment that will allow an employee to practice his or her religion.

Examples of some common religious accommodations include flexible scheduling, voluntary shift substitutions or swaps, job reassignments, and modifications to workplace policies or practices.
...
An employer does not have to accommodate an employee's religious beliefs or practices if doing so would cause undue hardship to the employer. An accommodation may cause undue hardship if it is costly, compromises workplace safety, decreases workplace efficiency, infringes on the rights of other employees, or requires other employees to do more than their share of potentially hazardous or burdensome work.

It is a paradox under US law, but a "reasonable accommodation" for a small group of religious workers may become an "undue hardship" if the proportion of workers needing the accommodation rises enough, which is probably what happened here.