A lawyer for Viktor and Amalija Knavs said the Slovenian couple took the citizenship oath on Thursday in New York City.
"CHAIN MIGRATION must end now!" he tweeted.
Wildes told ABC News "they applied on their own".
When the Times asked Wildes if the Knavs obtained their citizenship through family-based immigration ― often pejoratively referred to as "chain migration" ― Wildes was vague.
The Times noted that the couple would have to have their green cards for five years to become eligible for citizenship.
Their lawyer said the couple had met the five-year requirement, but added, "I can't give further comment".
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Karim said that, as a result, "the Conservative party today has to decide whether it will be a genuine one nation political force or an English nationalist movement".
The first lady's office declined to comment.
"I believe strongly in the principles of family reunification, which is a bedrock of immigration policy and law and has brought millions of people happily to our shores", Wildes said.
President Trump has railed against family-based or "chain" immigration in the past.
Trump's plan, which Congress has resisted, would limit immigrants like his wife to sponsoring only their spouses and underage children to join them in the USA, not their parents, adult children or siblings. Trump has advocated a "merit-based" system, but has not proposed any method of admitting immigrants to the U.S. to replace those categories. He also called for eliminating a visa lottery program for people from countries under-represented in the U.S. Experts estimate that could cut overall immigration to the USA by 40% to 50%, if those green cards are not reallocated to another category.
The Knavses' citizenship ceremony was kept hush-hush at the Jacob K. Javits Federal Building.
She settled in NY in 1996 and met Trump two years later.
Wildes wouldn't say how long the Knavses have lived in the US.
They raised Melania in the rural industrial town of Sevnica while Slovenia was under Communist rule.