Bipartisanship is in short supply these days, but a brief before the Supreme Court in a pending immigration case shows that key members of Congress from both major parties can agree on something.

Five senators — three Democrats and two Republicans — joined in a Nov. 4 brief opposing the Obama administration’s position on the Child Status Protection Act (CSPA), a 2002 law aimed at keeping immigrant families together.

The lawmakers filed their brief in Mayorkas v. de Osorio, set for argument on Dec. 10. The case involves efforts by a U.S. citizen to obtain visas for her daughter and the daughter’s family in El Salvador — a benefit available to the families of immigrants who have become U.S. citizens or hold permanent legal resident status. Because one of the daughter’s sons “aged out” by turning 21 while the application was pending, he had to stay behind while his family moved. The son, Melvin Cuellar de Osorio, has been waiting for the visa for 15 years. The law at issue allows certain categories of aliens who turn 21 to retain their place in line, so to speak, but the question before the court is how broadly the law sweeps.

The U.S. Court of Appeals for the Ninth Circuit sided with the family, finding that the act has an unambiguously broad scope. But the U.S. solicitor general’s appeal to the Supreme Court on behalf of Alejandro Mayorkas, director of U.S. Citizenship and Immigration Services, argues for a narrower reading embraced by the U.S. Board of Immigration Appeals. The government argues that if too many aliens retain their favorable place in line when they turn 21, they would “substantially disrupt the immigrant-visa system” by increasing the wait time for others.

All the senators who filed the bipartisan amicus brief were in Congress when the law passed in 2002. Their “unmistakable purpose” in passing the law, the brief says, was “to protect all children who seek to immigrate to this country from the consequences of ‘aging out,’ that is, turning 21 before a green card is available for them.” They accuse the solicitor general of trying to “muddle the clarity” of the law, adding: “This Court should not allow the Solicitor General to introduce ambiguity into the CSPA where none exists.”

Democrats Dianne Feinstein of California, Robert Menendez of New Jersey and Charles Schumer of New York were joined by Republicans Orrin Hatch of Utah and John McCain of Arizona. Republican Kansas Governor Sam Brownback, formerly a senator, also signed the brief.

“The fact that it has folks from both sides of the aisle may make the brief unusual, but it came about because of the bipartisan nature of the legislation,” said Scott Martin of Gibson, Dunn & Crutcher, counsel of record on the amicus brief. “It is just as bipartisan now as when it was passed.”

When Congress passed the CSPA to deal with the “aging out” problem, it did not intend for families like the de Osorios to “suffer this heartrending separation,” according to the main brief filed on the behalf of the family, authored by Mark Fleming of Wilmer Cutler Pickering Hale and Dorr.

Fleming said in a written statement, “We are delighted that this bipartisan group of leaders, from across the political spectrum, came together to explain that Congress meant what it said: that parents should be able to immigrate together with their children, without having to leave a child behind simply because she turned 21 while they were waiting to come to America.”

The law, Fleming said, “was meant to support fairness and family unity in immigration, and there is no reason not to apply its benefits to everyone.”

Contact Supreme Court correspondent Tony Mauro at tmauro@alm.com.