I think you have two possible claims, although both of them need further information. The first one is forced overtime and the second is religious discrimination.
Forced overtime might apply if the employer is holding you after hours, but overtime laws trigger only if you are forced to work over eight hours a day. The overtime laws won't stop your employer from forcing you to attend these...sessions, but they will force your employer to pay extra for attending them.
As for religious discrimination, anti-religious discrimination laws in the United States focus on preventing employers from infringing on the rights of employees to practice their religion. Although the laws do restrict an employer from forcing religion on employees, the cases are generally better if the employee already has a faith and the employer is trying to change that faith. The definition of religious discrimination in the legal system often precludes non-believers from bringing claims simply because an employer wants faith in the workplace.
It is also important to note that anti-discrimination laws trigger based on the number of employees a company has. The typical law for a case like this, the Civil Rights Act of 1964, triggers when a company has 15 or more employees. This doesn't have to automatically disqualify a case like yours, but you have to extend the definition of "employee" here in order to meet the 15 employee requirement if you want to bring a claim under the Civil Rights Act.
Finally, you should present your case to the Equal Employment Opportunity Commission to see if you can obtain a right to sue letter if you want to bring a religious discrimination claim. If you want to pursue forced overtime or an employment practice other than discrimination, you must go to the National Labor Relations Board. Best of luck.
I am not an attorney. Please see a lawyer for legal advice.
(removed)