As the White House prepares to issue an executive order that would bar federal contractors from discriminating on the basis of sexual orientation or gender identity, polls show that many Americans believe it’s already illegal to fire someone for being gay. In most states, it is not. A bill that would have offered lesbian, gay, bisexual, and transgender employees federal protections—the Employment Non-Discrimination Act—passed the Senate last year, but it looks dead in the House.

So let’s say a gay person just came out to his boss—and  got fired because of it. Is that legal? It depends.

What state are you in?
Most U.S. states lack explicit legislation barring discrimination against LGBT employees; current U.S. law is uneven, limited, and ambiguous. Only 21 states and the District of Columbia bar firing employees for their sexual orientation. Of those, 18 (and again, Washington) also ban firing transgender employees. California and Colorado have bans on orientation and gender identity discrimination; New York and Wisconsin have the former but not the latter; Florida and Pennsylvania have neither.

What city?
Nearly 200 municipalities—including cities in some of those 29 states without LGBT discrimination laws, such as Philadelphia, Cincinnati, and Phoenix—have banned such discrimination within their boundaries.

Is the company very small?
If so, it might be exempt from state discrimination protections: While Connecticut’s law covers any company with three or more employees, for example (PDF), statutes in Illinois, Maryland, Nevada, and New Mexico don’t kick in until a company has at least 15 workers.

Is the worker covered by a union contract?
For employees under union contracts or other legally binding employment agreements, getting fired for sexual orientation or gender identity could provide grounds for legal action under reasonable cause clauses, according to Christy Mallory, senior counsel at UCLA’s Williams Institute.

Or a public employee?
Government workers have greater protection against being purged for their sexuality than those in the private sector. In 1998, Bill Clinton banned firing federal workers for being gay; in 2011 the Obama administration directed agencies to “ensure a non-discriminatory working environment” for federal workers regardless of gender identity.

In 11 of the 29 states without LGBT protections, governors have issued executive orders or policies that prohibit discrimination against public employees based on sexual orientation—protections that can be a step toward passing broader legislation. Houston Mayor Annise Parker issued an order banning anti-LGBT discrimination in public employment in 2010, and last month she secured city council passage of a bill covering the private sector, following a contentious fight.

Is the employer a government contractor?
Even though workers at private contractors aren’t employees of the government, public agencies have a long history of conditioning contracts on non-discrimination. The coming executive order will ban discrimination against LGBT workers by federal contractors.

Or a religious group?
The big question about that promised executive order is whether it will include an exemption for religious groups. The language currently on the books dates to an executive order (PDF) issued by President George W. Bush, which states that religious contractors retain the right to employ only “individuals of a particular religion” if they so choose. That, suggests Human Rights Campaign Fund Vice President Fred Sainz, is ambiguous enough that “it could potentially be used as a cudgel against LGBT people.”

Where’s all this going? 
In a little-noticed 2012 ruling, the federal Equal Employment Opportunity Commission concluded that discrimination against transgender people is already illegal under federal law. That decision—spurred by the case of Mia Macy, a transgender woman who applied to work at the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives—concluded that such firings were a form of sex discrimination and are prohibited under the 1964 Civil Rights Act.

That EEOC ruling relied on the Supreme Court’s 1989 Price Waterhouse (PDF) decision, which found that sex-stereotyping can be evidence of sex-discrimination. Using similar logic, notes Mallory, attorneys have argued in recent years that sexual orientation discrimination is inherently a form of gender discrimination “because it’s based on this idea that one gender has to be with another gender.” Earlier this year, a Library of Congress employee argued that he was punished because his “status as a homosexual male did not conform to [his manager’s] gender stereotypes associated with men.” A federal district judge is allowing the case to proceed.