WASHINGTON >> The parents of the first lady, Melania Trump, have obtained lawful permanent residency in the United States, a lawyer for the couple confirmed today, but it remains unclear how or when the couple received their green cards.

The lack of clarity about when and how Viktor and Amalija Knavs obtained their legal residencies raises questions about whether the couple secured their residency through family-based immigration, which President Donald Trump calls chain migration and has said he wants to restrict. Immigration experts said it would have been the most direct, and most likely, way for Melania Trump’s parents, formerly of Slovenia, to get their green cards.

Their immigration lawyer, Michael J. Wildes, declined to offer any details.

“It’s a privilege to help this family, but I have to respect their privacy as well,” Wildes said in a brief interview.

“Immigration is in our DNA,” he added. “We have to take great pride, no matter where somebody hails from, in that legacy.”

Stephanie Grisham, a spokeswoman for Melania Trump, wrote in an email that she would not comment on the first lady’s parents because “they are not part of this administration, and deserve their privacy.” The Washington Post first reported the Knavses’ immigration status.

Under family-based immigration, adult U.S. citizens can petition for residency for their parents, adult married children and siblings. Trump would limit that to parents and children under 21.

In the Knavses’ case, Melania Trump, who became a citizen in 2006 after obtaining a green card, would have sponsored them.

“It would be odd if she sponsored her parents and didn’t want to talk about that because it’s a fairly routine thing,” said Hiroshi Motomura, a law professor at the University of California, Los Angeles, who specializes in immigration law. “It only becomes sensitive if her husband is taking a position against this.”

Both of Melania Trump’s parents have been seen at White House events, celebrated Thanksgiving at Mar-a-Lago, Trump’s Florida estate, and reportedly spend much of their time with the Trump family. Questions about their immigration status were raised in recent months as the administration emphasized stricter immigration reform.

About 7 million of the 11 million immigrants who obtained green cards between 2007 and 2016 did so through familial relations, according to data from the Department of Homeland Security.

“In some ways, lawful permanent resident status is the best of all visas,” said Kevin R. Johnson, the dean of the law school at the University of California, Davis, who has taught immigration law. “It’s the Cadillac of immigrant visas because it allows you a path to citizenship.”

But Trump has vilified the program as a way for terrorists to enter the United States and has called for aspects of the program to be eliminated as part of immigration reform.

“CHAIN MIGRATION must end now!” he wrote on Twitter in November. “Some people come in, and they bring their whole family with them, who can be truly evil. NOT ACCEPTABLE!”

It also might have been possible, Johnson said, for the Knavses, both in their 70s, to obtain residency through an investment visa or a work visa, although the latter would involve employer sponsorship. Victor Knavs, a former traveling car salesman, and Amalija Knavs, who used to design patterns for children’s clothes, both appear to be retired.

Immigrants can also apply for asylum or enter the diversity lottery, paths that offer limited numbers of visas. Trump has also criticized the diversity lottery, which allows admission to immigrants from countries that do not send many people to the United States.

“If somebody came to me and asked me how to become a citizen, the first question I would ask is ‘Do you have an American citizen as a relative?’” said Theresa Cardinal Brown, the director of immigration and cross-border policy at the Bipartisan Policy Center in Washington. “That is the fastest and most direct route to getting a green card.”

In his State of the Union address, Trump described a four-pillar immigration plan and continued to criticize the family-based immigration program, eliciting boos from Democrats in the chamber.

“Under the current broken system, a single immigrant can bring in virtually unlimited numbers of distant relatives,” he said. “This vital reform is necessary, not just for our economy, but for our security, and our future.”