Actually the letter explicitly states:
It is my sincere religious conviction that I cannot join or financially support an employee’s union. ... it is based on principles I have found in God’s Word and as taught by my church. The attached letter from my church pastor and my denomination’s official position statement will verify this.
I know of NO Christian denomination (except maybe Amish???) conservative or liberal, which forbids membership in a labor union or has an "official position statement" about the subject.
I would be highly suspicious of any pastor or denomination who would take a position either--given that anything resembling unions were unknown in Bible times.
To me this letter is a bunch of nonsense--as you have the natural right to work, and be a part of a union, or not, for ANY REASON regardless of religious conviction.
I understand the effort to get around unjust laws using religion--but, it appears to me to be a misuse of religion.
That letter was pulled from a Christian site as an example. Here is actually the requirements of the law and how it has been interpreted:
Q: Who qualifies as a “Religious Objector”?
A: Title VII of the Civil Rights Act accommodates persons who object on religious grounds to the payment of union dues by allowing them to give to a charitable organization as a substitute form of payment. The courts have uniformly interpreted this provision to require accommodation through substitute charitable payment.
a.) What if the union requests to see my church doctrine or a letter from my pastor?
Unions cannot require objectors to submit church doctrine statements that demonstrate religious convictions against supporting unions. Two court decisions have declared a union objector needs only to explain his/her sincere religious objection and it does not have to be supported by any official church doctrine. The employee simply has an obligation to provide a sufficient description of their religious belief or conviction to prove that it is in fact a sincere belief. For example, you can quote religious scripture or discuss religious experiences (e.g., “God convicted me of . . .”).
Unions also cannot request to see letters from clergy. In some instances, uncooperative unions have tried to discourage workers from transferring their union dues to charities by demanding statements from clergy or church leaders. The courts have ruled in favor of the employees, stating that they must only thoroughly explain why it is against their earnest religious beliefs, nothing more.