"While we have in the past told you of our cooperation with the government's investigation, our cooperation is no longer unconditional," Cohen's hedge fund SAC Capital Advisors said in a statement distributed to its investors.
The New York Times reported Monday the message in SAC's response -- the message reading between the lines -- is that Cohen would likely invoke his right not to testify to avoid self-incrimination.
In the past, Cohen has cooperated. He agreed to provide authorities with a civil deposition in 2012 in an insider trading case involving portfolio manager Mathew Martoma, the Times reported.
To date, four former SAC employees have pleaded guilty to insider trading charges, while two others, Martoma and Michael Steinberg, are contesting the charges.
SAC manages about $16 billion, more than half of which belongs to Cohen and to SAC employees, which number about 1,000.
Investors, meanwhile, have withdrawn about $1.7 billion from the fund since its legal troubles began, leaving the firm to manage about $6 billion of outside money.
Some of the details of the case suggest authorities are building up a case against the hedge fund itself, which is much more rare than cases against individual traders or executives.
Jonathan Gasthalter, a spokesman for SAC, declined to comment, as did J. Peter Donald, a spokesman for the FBI, and Ellen Davis, a spokeswoman for federal prosecutors' office in New York.