Originally posted by robbie carrobie
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances
Does this amendment solely apply to the government and areas of government ju ...[text shortened]... ion and thus private organisations are therefore free to discriminate on any basis they see fit?
The First Amendment doesn't outlaw discrimination except on religious grounds. Other Amendments (mainly the 14th and 5th) address discrimination in other forms.
But the premise of your question is correct. The Constitution mainly only applies to government action. It does not prohibit discrimination by private citizens or companies (perhaps the 13th Amendment's ban on slavery could be used to prohibit some forms of private discrimination, but this area has not been explored thoroughly by the courts).
The prohibition on private discrimination, principally in the areas of employment and public accommodations, come via federal and state statutes, such as the Civil Rights Act of 1964. Ironically, Congress has the power to pass these sorts of civil rights laws mainly under its power to regulate commerce, as the constitutional equal protection clause applies only to government action.
When it comes to private action not covered by statute, there is no prohibition on discrimination. For example, if I want to exclude black people from my football-watching Sunday afternoon parties, that is not only allowed, but also my right under freedom of association. Even a large organization, such as the buy scouts or Augusta National Golf Course, are allowed to discriminate if they so choose because they're not public accommodations.
See Boy Scouts of America et al. v. Dale, 530 U.S. 640 (2000).
Edit: Yes, "my club my rules" works unless you're covered by the civil rights acts, as in the case of many employers and public accommodations, such as restaurants.