You don't have to prove discrimination, only that the rules have a disparate impact on an aggrieved group.
In
United States employment law, the doctrine of
disparate impact holds that employment practices may be considered discriminatory and illegal if they have a disproportionate
"adverse impact" on members of a minority group. Under the doctrine, a violation of Title VII of the
1964 Civil Rights Act may be proven by showing that an employment practice or policy has a disproportionately adverse effect on members of the protected class as compared with non-members of the protected class.
[1]
The doctrine prohibits employers "from using a facially neutral employment practice that has an unjustified adverse impact on members of a protected class. A facially neutral employment practice is one that does not appear to be discriminatory on its face; rather it is one that is discriminatory in its application or effect."
[2] Where a disparate impact is shown, the plaintiff can prevail without the necessity of showing intentional discrimination unless the defendant employer demonstrates that the practice or policy in question has a demonstrable relationship to the requirements of the job in question.
[3] This is the so-called "business necessity" defense.
It can easily be stretched to show that a public bar discriminates under the same doctrine.. Basically, if you are white and want to hang out with whites in a public place, you are guilty of discrimination until proven otherwise.