What the Federal law says. 

"The federal law does not prohibit discrimination based on sexual orientation, so 
***gays are not a protected group*** under the federal law."

Note:  Individual state laws can override that. 
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Reference
1) https://en.wikipedia.org/wiki/LGBT_rights_in_the_United_States

2)https://www.americanbar.org/publications/human_rights_magazine_home/human_rights_vol31_2004/summer2004/irr_hr_summer04_protectlgbt.html