Well, Mike's post assumes that an employee does sue -- which has happened in the past.
If an employee does sue, there are two possibilities.
First, the employee is, or at least was, a Scientologist. Even if so, an employer cannot coerce an employee to participate in religious services even if the employer and the employee share the same religion. A Catholic employer cannot coerce a Catholic employee to participate in Mass as a condition of employment. Likewise, A Scientologist employer cannot coerce a Scientologist employee to participate in Scientology religious courses or auditing as a condition of employment.
Second, the employee is not a Scientologist. You note the qualifying language "who are Scientologists." Still, in this case the non-Scientologist employee can argue that the employer was illegally trying to force his "Scientologist" employees to participate in Scientology religious services, and he was pressured to both join the Church of Scientology and participate in order to improve the "stats" of his Scientologist in the official Church of Scientology "game."
The bottom line is that one can use the promo to argue that the Church of Scientology is promoting and encouraging illegal conduct by employers who are Scientologists. Such illegal behavior can victimize employees who are Scientologists who do not want to participate in Scientology religious services, as well as non-Scientologist employees who feel pressured to join the Church of Scientology and participate in such services.