Here are two plausible necessary conditions for a law to violate freedom of religion or freedom of conscience:
- Legislation L violates x's freedom of religion only if L requires x to do something that is contrary to the requirements of x's religion.
- Legislation L violates x's freedom of conscience only if L requires x to do something that is contrary to the requirements of x's conscience.
Let me start with (1). There is a simple counterexample. Consider legislation prohibiting public religious worship on Saturdays. Such legislation seems to be a paradigm of legislation that violates the religious freedom of Jews. But it is my understanding (and if the understanding is flawed, just make this a hypothetical) that Judaism does not require public worship on Saturdays--the requirements of prayer do not have to be fulfilled in Synagogue worship. Hence (1) is false.
Now consider (2). Suppose that Sam is a typical vegetarian on grounds of conscience. Now, consider legislation M1 that requires everyone to eat meat on New Year's Eve, under penalty of a week in jail. This legislation is a paradigmatic case of a law that violates Sam's freedom of conscience. (Note: I am not taking it to be clear that "violates x's freedom of conscience" entails that the legislation is unjustified; obviously that legislation violates someone's freedom of conscience is a strong reason against having such legislation, but since consciences can be mistaken in all sorts of spectacular ways, there may be times where such legislation is justified.) But note that except in really weird scenarios, M1 isn't like that.)
But now consider legislation M2 that is just like M1, except that now the penalty is death. Surely if M1 violates Sam's freedom of conscience, so does M2. But Sam is a typical vegetarian. And typical vegetarians, I think, hold that it is permissible to eat meat when the alternative is death. Thus, M2 does not require Sam to do anything that is contrary to the requirements of his conscience: it requires him to eat meat, but eating meat is permissible given M2.