WASHINGTON, D.C. - An attorney for First Lady Melania Trump and her family has confirmed her parents, Viktor and Amalija Knavs, are "lawfully admitted into the United States as permanent residents," which has prompted questions over how that happened.

"Family reunification has been a principal of immigration and has been for a long time," said Ruben Reyes, a local immigration attorney.

Melania Trump and her family originate from Slovenia.

President Trump has been vocally critical of an immigration process called "family reunification," also known as "chain migration."

The process permits a U.S. citizen to sponsor immigration family members in order to gain legal status. Melania Trump became a citizen in 2006 after marrying President Trump.

"It would be highly likely that (Melania) would, in order to maintain the unity of her own family, petition for her parents," Reyes said, "a process that usually takes about a year or so."

This option would take the least amount of time compared to other possibilities, Reyes said, like obtaining a business visa.

"It's least efficient. It would require them to have a certain skill set before they even apply," he said.

The attorney for the family declined to comment further on the details of how the couple obtained their green cards and did not disclose when they would be sworn in as citizens.