The Securities and Exchange Commission is taking Bill Ackman seriously.

Days after the hedge-fund mogul wrote the regulator and complained about alleged insider-trading violations by George Soros’ family fund regarding its trading in Herbalife, the SEC took action.

An SEC lawyer has contacted at least one person who spoke with Soros Fund Management portfolio manager Paul Sohn, who was driving the firm’s Herbalife investment, The Post has learned.

Bill Keep, the dean of the College of New Jersey, who is an expert on pyramid schemes, was recently questioned by Liora Sukhatme, a lawyer in the SEC’s enforcement area.

Sukhatme asked Keep about a meeting he had with Sohn on June 26, he said.

Keep, who has ties with the Federal Trade Commission, declined to elaborate on his SEC chat. Sukhatme did not return a call for comment.

Ackman famously took a $1 billion short against the multilevel marketing company last year, saying it was a pyramid scheme. Herbalife has denied the accusation.

As first reported by The Post, Ackman filed a complaint with the SEC against Soros and unidentified co-conspirators, alleging the firm broke insider-trading rules by tipping hedge funds at so-called idea meetings about its Herbalife share purchases.

Sohn told the investors at the meetings that Soros’ fund was buying shares of Herbalife and would soon report a nearly 5 percent stake in the company, Ackman alleged.

Perry Capital reportedly took a big stake in Herbalife following Soros’ investment.

Neither Soros nor Perry would comment on whether the SEC contacted them on the matter.

Keep said Sohn wanted to know the likelihood of an FTC probe. He said he told the Soros fund executive an FTC probe “would be expensive and time consuming.”

By the end of June — four days after Sohn met with Keep — Soros had amassed a 4.9 percent stake in Herbalife, making it the third-largest position in the fund, according to an SEC filing.

Since meeting with Sohn, Keep has been quoted as saying that an FTC investigation was “not probable at this point.”

More likely, Keep said, was that the FTC would first revise a 2004 ”advisory” letter, which he thinks has been misconstrued, leading to confusion over what constitutes a pyramid.

However, after reading Ackman’s second-quarter letter, in which the activist claimed to have made “material” progress with regulators, Keep has changed his tune. He now sees some form of regulatory action to be more likely.

mcelarier@nypost.com