In September 1966, a Florida woman named Ida Phillips drove to a missile plant in Orlando to apply for a job on the assembly line.* It paid more than double what she was making as a waitress, and she had seven kids to support. But once the receptionist found out that Phillips had a child in preschool, she wouldn’t even give her an application. The company, Martin Marietta (now known as Lockheed Martin), didn’t hire women with kids that young, though men with children the same age were free to apply—between mothers and fathers, the company assumed it was mothers whose attendance would suffer because of a sick child or lack of childcare. And even if they made it to work, the thinking went, mothers would just be too distracted by thoughts of the home front to get the job done.

While those assumptions still bedevil working mothers, explicit bans like Martin Marietta’s are now against the law. That’s because 45 years ago today, the Supreme Court heard oral arguments in Ida Phillips’s case.

The law under which Phillips sued, Title VII of the landmark 1964 Civil Rights Act—the “title” outlawing employment discrimination because of race, color, national origin, religion, and sex—had never been interpreted by the Court. That its first opportunity to do so arose in a case brought by a woman was ironic, given that Title VII’s ban on unequal treatment of women had been added to the legislation at the last minute. Many, including the Equal Employment Opportunity Commission, the federal agency charged with enforcing the new law, were skeptical that it was meant to do much of anything. Indeed, not long after Title VII was enacted, the EEOC’s executive director derided the sex provision as a “fluke” that was “conceived out of wedlock.”

Complicating Phillips’s case was the fact that Martin Marietta had produced personnel data showing that it overwhelmingly hired women for the job Phillips had been denied. So the company didn’t ban all women—which unquestionably would have been discrimination “because of sex”—but just one category of women, namely mothers of young children. Was discrimination “because of motherhood” equally illegal?

At the podium arguing Phillips’s case was William Robinson, a young attorney with the NAACP Legal Defense and Educational Fund. Although its mission was to advance the civil rights of African Americans, and Phillips was white, the group’s leadership understood the high stakes of Phillips’s case. For one thing, black mothers were nearly twice as likely to work as white mothers were, so a decision upholding Martin Marietta’s rule would be economically disastrous for African American families. For another, if the Court found the company’s rule nondiscriminatory because it only excluded some women, Title VII would surely die by a thousand cuts. Employers could re-impose many Jim Crow-era rules: Instead of barring all African Americans from applying, they simply could ban those who, for instance, didn’t have a high-school diploma or achieve a certain score on a shoddily-designed aptitude test.

As it turned out, Robinson didn’t have to spend a lot of time in his arguments detailing these potentially dire consequences. Instead, he had to contend with the fact that some justices held many of the same stereotypes about women’s inherent interests and abilities that underpinned Martin Marietta’s policy. “Does the law require that the employer give the woman a job of digging ditches and things of that kind?” asked Justice Hugo Black. Or, Black continued, could an airline “decide that they only wanted to have the job position of stewardesses” and not hire any men because “customers like women better in that place, younger women obviously”? Justice Harry Blackmun, who just three years later would author the majority opinion in Roe v. Wade, asked Robinson to “educate me”: “[S]uppose a hospital for years had employed nothing but female registered nurses,” he hypothesized, “and then today after the passage of this Act, a male nurse applicant comes along. Do I understand your interpretation of the Act to be that just because they have always had female RNs and like them and got along well, they could not refuse to hire the male nurse?”

Chief Justice Warren Burger also appeared uneasy with the notion that Title VII required employers to assume women and men were equally equipped to do most jobs. Was it the case that if a federal judge like him “would decline to hire a law clerk who had an infant child, a lady law clerk, but was willing to hire a man whose wife had infant children,” then he “would be in violation of the statute?” No, answered Robinson, because the law didn’t apply to federal employers (a gap later closed by a 1972 amendment). Burger earned a laugh from the gallery with his relieved reply, “I am sure, it doesn’t apply to federal judges.”

Later, when Martin Marietta’s counsel explained that the assembly-line job denied to Phillips was not “heavy work” but rather “intricate work” involving “small electronic components,” Burger stated that that was surely why women comprised the bulk of the company’s workforce. “[W]omen are manually much more adept than men and they do this work better,” he opined, adding, “Just the same reason that most men hire women as their secretaries, because they are better at it than men.”

That the Chief Justice of the Supreme Court apparently had no qualms about declaring women to be inherently better secretaries than men spoke volumes about how little Title VII had done in its six-year existence to uproot, or at least to stigmatize, the cultural biases motivating a lot of sex discrimination.

Shortly after the oral argument, the Court issued its unanimous decision. Like so many Court rulings, it was a mixed bag. In one sense, it was a big win for Ida Phillips, and for all employees covered by Title VII: The Court agreed that refusing to hire mothers (or any other sub-group of protected workers) was just as discriminatory as if Martin Marietta had refused to hire any women at all. That expansive definition of Title VII’s coverage still stands. But the Court apparently agreed that Martin Marietta’s concerns about mothers’ job commitment weren’t off-base; it sent the case back to the lower court for a trial, so the company could present any evidence it could muster that mothers in fact had higher rates of absenteeism, or made more mistakes, or took more phone calls during the work day, than non-mothers. Title VII allows employers this loophole. If they can prove that only one sex could do a certain job—say, that only a woman could portray Cleopatra in a stage production—then it isn’t illegal to restrict that job to men only or women only. Notably, the law doesn’t permit this exception for race discrimination, preventing employers from ever deeming certain jobs “for whites only” or “for blacks only.”

As it turned out, Martin Marietta had no appetite for a trial, and settled Ida Phillips’s case soon after. (She used the modest proceeds to give her daughter a down payment on a house, buy herself the first air conditioner she’d ever had, and take her youngest daughter—the one who had cost her the job at the company—to Disneyworld.) And subsequent court decisions have departed from the Supreme Court’s interpretation of Title VII’s loophole; its willingness to give Martin Marietta a chance to use a stereotype to justify discrimination against all mothers has not, for the most part, prevailed.

The reality, though, is that motherhood continues to pose a stubborn barrier to working women. When Phillips applied to work on that assembly line, only about 25 percent of mothers with children under six were in the workforce. Today, that number has more than doubled, to nearly 70 percent. Yet studies confirm that mothers are still viewed as less committed to their jobs than men. This “maternal wall” results in lower pay for mothers than for fathers, fewer opportunities for advancement, and even—just as Ida Phillips faced—outright job denial. True, the biases on display at that oral argument 45 years ago may not be voiced as openly or as often, because thanks to Title VII, they’re recognized as illegal. But make no mistake: They’re still there.

* The sub-headline to this article originally stated that Phillips v. Martin Marietta Corporation was decided 50 years ago. We regret the error.