Washington (CNN) Four leading Democrats are demanding a new FBI investigation into a Florida woman's apparent ties to Donald Trump, focusing on whether she illegally sought to leverage her relationship with the President by selling access to Chinese clients.

The Democrats -- Sen. Mark Warner, the top Democrat on the Senate Intelligence Committee, House Intelligence Chairman Adam Schiff, Sen. Dianne Feinstein, the top Democrat on the Senate Judiciary Committee and House Judiciary Chairman Jerry Nadler -- are calling on the FBI to conduct criminal and counterintelligence probes into allegations of human trafficking, foreign lobbying and potential campaign finance violations against Cindy Yang, the founder and former owner of a chain of Florida massage parlors.

The Democrats' letter says Yang's website used to offer clients "the opportunity to interact with the President" and other top political leaders, and they point to public reports saying she has been a frequent guest of Trump's, including at his Mar-a-Lago estate.

"Although Ms. Yang's activities may only be those of an unscrupulous actor allegedly selling access to politicians for profit, her activities also could permit adversary governments or their agents access to these same politicians to acquire potential material for blackmail or other even more nefarious purposes," the lawmakers wrote

The letter, addressed to FBI Director Christopher Wray, Director of National Intelligence Dan Coats and Secret Service Director Randolph Alles, asks for responses by Thursday to a number of questions about her contacts with Trump.

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