As of Tuesday evening, if someone is fired in the United States for being gay (which there are no laws against in more than half the states), they can now file a discrimination lawsuit and reasonably expect it to succeed.

That's because a federal appeals court in Chicago ruled Tuesday that the 1964 Civil Rights Act means workers can't be fired based on their sexual orientation. It's not the first court to decide this, but it is the highest.

LGBT advocates expect that sooner or later, the question of whether U.S. civil rights law applies to gay, lesbian, bisexual and transgender people will reach the U.S. Supreme Court, which has the power to overturn a patchwork of nondiscrimination laws (or lack thereof) in 50 states, just like it did when it legalized same-sex marriage across the nation in 2015.

To get a better sense of the changing legal landscape on LGBT rights, we called up James Esseks, director of the ACLU's Lesbian Gay Bisexual Transgender & HIV Project and an advocate for LGBT protections. Our conversation has been lightly edited for length and clarity.

THE FIX: Does this decision mean LGBT people can get married on a Saturday and no longer fired on a Monday — a disparity in federal law that LGBT advocates often highlight?

ESSEKS: Yes. In our view, it's long been true that lesbian, gay, bisexual and transgender people are protected under the federal civil rights law. Discrimination against LGBT people is, by its very definition, sex discrimination. What's happening now in the courts is an emerging recognition that that's right.

Help me break down a key argument from Tuesday's ruling, which decided Kimberly Hively was improperly passed over for a teaching job in Indiana because she's a lesbian. Chief Judge Diane Wood wrote: "Hively represents the ultimate case of failure to conform to the female stereotype … she is not heterosexual. Hively’s claim is no different from the claims brought by women who were rejected for jobs in traditionally male workplaces, such as fire departments, construction, and policing."

She's saying: When an employer decides that it doesn't want a lesbian on its workforce, it is taking her sex into account, because you can't understand what a lesbian is unless you understand that it's a woman who forms intimate relationships with a woman. If she were a man who formed intimate relationships with a woman, this employer wouldn't have any problem with her. And so the only difference is the sex of the employee. That, says the 7th Circuit Court — we think correctly — is sex discrimination. That's what the civil rights laws were designed to eradicate.

But the 7th Circuit decision is not the law of the land?

The 7th Circuit creates laws for three states: Indiana, Illinois and Wisconsin. If you say, "Hey, my employer discriminated against me because I'm a lesbian," in Indiana, Illinois and Wisconsin there's no question that's [illegal in those states]. The only question in the court will be: "Did they fire you because you're a lesbian, or did they fire you for some other reason?"

But this decision has persuasive authority elsewhere. More people who have suffered employment discrimination in other parts of the country can use this decision as precedent: "If I can prove they did it because I'm gay, that's sex discrimination, and it violates federal law. And yes, I have to prove it's discrimination, but I don't have to fight about whether I'm covered under the law."

But other federal courts have ruled that sex discrimination laws don't apply to LGBT people.

We're not at the end of the development of this law. But this is a big moment. The 11th Circuit, which sits in Atlanta, just had a panel decision by three judges that went against. But I believe there is going to be a request that the full court there take up this question, just like the 7th Circuit did. There's a similar situation in New York.

We're in a moment where a series of very important, influential courts either have taken a look at this question or are poised to. I think we're at the beginning of a sea change on this issue in the federal courts.

There's a trend line here, and it's going toward greater protections for LGBT people on civil rights.