SAC Capital Advisors LLP is under investigation by a powerful U.S. Republican Senator for 20 possible instances of insider trading, the Wall Street Journal reported on Saturday, citing unnamed sources familiar with the situation.

Charles Grassley, who heads the Senate Judiciary Committee, last month asked the Financial industry Regulatory Authority for details on any suspicious trading at Steven Cohen's $13 billion hedge fund since 2000.

Last week Finra provided Grassley with about 20 instances where SAC's trades took place ahead of market-moving news or were otherwise suspicious enough to merit referral to the Securities and Exchange Commission's enforcement staff, the Wall Street Journal said.

It was not clear if the trades had been referred to the SEC, and authorities have not alleged wrongdoing by SAC or Cohen, the report said.

The government has been investigating current and former SAC employees since prosecutors announced a huge insider trading case involving the Galleon Group in October 2009 and SAC Capital employees Donald Longueuil and Noah Freeman have pleaded guilty to charges.

Earlier this month Galleon Group founder Raj Rajaratnam was convicted on insider trading charges in a sweeping government victory in the case.

Court filings also show that prosecutors are investigating trade accounts at SAC, including one tied to Cohen, SAC Capital's founder.

SAC representatives and Congressional investigators met in Washington on May 10 to discuss the matter, the report said.

At the meeting, SAC representatives suggested the investigators go easy on the hedge fund, saying it has internal procedures to track down and prevent illegal trading, according to the report.

Also at the meeting, Washington-based SAC Capital in-house lobbyist Michael Sullivan cited Cohen's civic-minded interest in purchasing a stake in the New York Mets baseball team.

We welcomed the opportunity to meet with the staff to educate them about the firm and our compliance efforts, and had an entirely appropriate, professional and cordial meeting, said SAC Capital spokesman Jonathan Gasthalter. We will continue to cooperate in any way we can.

Grassley's office was not immediately available to comment to Reuters.

(Reporting by Ann Saphir with reporting by Matt Goldstein)

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