The Supreme Court unanimously ruled on Monday that immigrants permitted to stay in the country temporarily are ineligible to pursue "green cards" for permanent residency if they entered the country illegally.

The ruling in Sanchez v. Mayorkas, authored by Justice Elena Kagan, could affect tens of thousands of immigrants currently living in the U.S. under Temporary Protected Status, the Associated Press reported.

The case was brought by Jose Sanchez and Sonia Gonzalez, a married couple from of El Salvador who entered the United States illegally in the late 1990s. Later, in 2001, the two were granted Temporary Protected Status in the U.S. after El Salvador was rocked by devastating earthquakes.

TPS is a status granted to foreign nationals from certain designated countries ravaged by armed conflict or natural disaster that allows them to live and work in the U.S. without being subject to deportation.

Then in 2014, Sanchez and Gonzalez applied for "green cards," or lawful permanent resident status, but were denied, and subsequently sued.

The Third Circuit Court of Appeals in Philadelphia, however, ruled against them, arguing that they were ineligible under federal immigration law, which requires applicants to have been "inspected and admitted" into the U.S, the New York Times reported.

In Monday's unanimous ruling, the nation's top court agreed with that decision.

"The question here is whether the conferral of TPS enables him to obtain LPR status despite his unlawful entry. We hold that it does not," wrote Kagan.

Kagan held that two parts of the immigration laws operate on separate tracks — one track allows some immigrants who entered the country legally to apply for green cards, and the other track allows immigrants, whether they entered legally or not, to pursue TPS.

Though the two tracks can sometimes merge, she noted, individuals who enter the country illegally do not become eligible for green cards because of their temporary status.

"Lawful status and admission, as the court below recognized are distinct concepts in immigration law: Establishing one does not necessarily establish the other," she wrote.

"The TPS program gives foreign nationals nonimmigrant status, but it does not admit them. So the conferral of TPS does not make an unlawful entrant ... eligible [for a green card]," she added.

There are an estimated 400,000 people with TPS in the country currently, and 85,000 of them have managed to adjust status, CNN reported.