The pair had been living in the United States on green cards sponsored by their daughter Melania.
Security guards and US Citizenship and Immigration Services workers in offices adorned with Donald Trump's portrait said they were unaware of anyone being sworn in there on Thursday.
Wildes said the term was a "dirtier" way of describing "a bedrock of our immigration process when it comes to family reunification", the Times reported.
In a phone call on Thursday evening, Wildes declined to comment on whether Viktor and Amalija Knavs support President Trump's push to curb family-based sponsorship.
During a bipartisan meeting with lawmakers in January, for example, Trump said, "Chain migration is bringing in many, many people with one, and often it doesn't work out very well". I've had the privilege of coming to this building for more than 30 years working with some of the finest families and individuals [.] This golden experiment, these doors that are in America, remain hinged open to attractive people as they have today.
Under immigration statutes, the Knavses would have needed to have their green cards for at least five years in order to apply for citizenship, along with fulfilling character, residency and civic knowledge requirements, it said.
They arrived and departed from a Manhattan federal building escorted by Homeland Security police.
"They have travelled a wonderful journey like many have, like millions have", said lawyer Michael Wildes. They had been living in the U.S.as permanent residents.
Indian batsmen need to learn from Virat Kohli to succeed in England
Anderson rued his side's poor catching and said England need to take their chances against a batsman of Kohli's calibre. But Stokes, who might not play the second Test owing to his court case, managed to nick out the edge England wanted.
Melania Trump became a citizen in 2006 after obtaining a green card.
It said it is unclear about when or how the couple received green cards.
Melania Trump's parents have been sworn in as USA citizens.
Melania Trump became a U.S. citizen after entering the country on an Einstein visa for "individuals of extraordinary ability" in 2001 as a model.
William White, a 74-year-old actor, said, with his eyebrows raised, "I'm happy for them".
The Knavs' immigration attorney accompanied the couple to the ceremony.
The Knavses raised daughter Melania in the city of Sevnica, while Slovenia was under communist rule.
She settled in NY in 1996 and met Trump two years later. Viktor was a vehicle dealer. Now, we're certain his shameless hypocrisy sees no boundaries.