According to the plaintiffs in U.S. Pastor Council et al. v. Equal Employment Opportunity Commission, et al., No. 4:18-cv-00824-O, In the United States District Court, Northern District of Texas, Fort Worth Division, who filed a motion for summary judgment on this issue last week, the answer should be yes.

In U.S. Pastor, the plaintiffs contend that Bostock’s interpretation of Title VII does not prohibit discrimination against bisexual employees (as opposed to homosexual or transgender employees specifically referenced in Bostock)as long as the employer regards bisexual behavior or orientation as equally unacceptable in a man or woman.  In support of their argument, the plaintiffs cite the following language from Bostock:

Take an employer who fires a female employee for tardiness or incompetence or simply supporting the wrong sports team. Assuming the employer would not have tolerated the trait in a man, Title VII stands silent. 

Bostock v. Clayton County, Georgia, 140 S. Ct. 1731, 1740 (2020).  Setting aside any personal beliefs or opinions regarding the Supreme Court’s decision, the plaintiffs’ argument appears misplaced based on Bostock’s logic. More specifically, the quote relied on by plaintiffs is cherry-picked from the opinion and omits the related logic which immediately follows:

But unlike any of these other traits or actions, homosexuality and transgender status are inextricably bound up with sex.  Not because homosexuality or transgender status are related to sex in some vague sense or because discrimination on these bases has some disparate impact on one sex or another, but because to discriminate on these grounds requires an employer to intentionally treat individual employees differently because of their sex.  

Id.  As the Court explained further:

An employer musters no better a defense by responding that it is equally happy to fire male and female employees who are homosexual or transgender.  Title VII liability is not limited to employers who, through the sum of all of their employment actions, treat the class of men differently than the class of women. Instead, the law makes each instance of discriminating against an individual employee because of that individual’s sex an independent violation of Title VII. So just as an employer who fires both Hannah and Bob for failing to fulfill traditional sex stereotypes doubles rather than eliminates Title VII liability, an employer who fires both Hannah and Bob for being gay or transgender does the same.

Id. at 1742-43.  Stated differently, it certainly appears the Court addressed and rejected the very argument the U.S. Pastor plaintiffs make.
Additionally, in their summary judgment motion, the U.S. Pastor plaintiffs contend that “Bostock did not hold that an employer violates Title VII whenever it discriminates on account of ‘sexual orientation,’” but this argument also appears to be contradicted by Bostock’s logic:

When we apply the simple test to Mr. Bostock—asking whether Mr. Bostock, a man attracted to other men, would have been fired had he been a woman—we don’t just change  his sex. Along the way, we change his sexual orientation too (from homosexual to heterosexual). If the aim is to isolate whether a plaintiff ’s sex caused the dismissal, the employers stress, we must hold sexual orientation constant—meaning we need to change both his sex and the sex to which he is attracted. So for Mr. Bostock, the question should be whether he would’ve been fired if he were a woman attracted to women. And because his employer would have been as quick to fire a lesbian as it was a gay man, the employers conclude, no Title VII violation has occurred.

While the explanation is new, the mistakes are the same. The employers might be onto something if Title VII only ensured equal treatment between groups of men and women or if the statute applied only when sex is the sole or primary reason for an employer’s challenged adverse employment action. But both of these premises are mistaken. Title VII’s plain terms and our precedents don’t care if an employer treats men and women comparably as groups; an employer who fires both lesbians and gay men equally doesn’t diminish but doubles its liability.

Id. at 1747-48.  Simply put, bisexuality, like homosexuality and transgender status, is by definition a form of sexual orientation.  And, according to Bostock, when an employer discriminates against an individual based on other types of sexual orientation, the action amounts to discrimination “based in part on that individual’s sex.”  Id. at 1743.  
In summary, and based on the reasoning in Bostock, the U.S. Pastor plaintiffs’ argument would create a difference without a distinction if the sexual orientation categories of homosexuality and transgender status are “inextricably bound up with sex” and therefore protected under Title VII, but the sexual orientation category of bisexuality is not.  Such a position would contravene Bostock’s reminder that, “[a]s enacted, Title VII prohibits all forms of discrimination because of sex, however they may manifest themselves or whatever other labels might attach to them.”  Id. at 1747.
It will certainly be interesting to see how the district court approaches such an argument.