(Reuters) - Hedge fund Omega Advisors Inc and its CEO Leon Cooperman received a Wells notice from the U.S. Securities and Exchange Commission in March this year, according to an investor letter viewed by Reuters.
While a Wells notice does not necessarily mean the recipients have violated any law, the SEC issues the letter to firms when it is planning to bring an enforcement action against them.
"I was subpoenaed by the staff to appear for an interview on March 11 and on the strong advice of my lawyers, I asserted my Fifth Amendment right not to testify," Cooperman, who runs the hedge fund, which has $7.4 billion under management as of Sept. 30, wrote in the investor letter.
Cooperman told CNBC that the Wells notice centered around trading related to Atlas Pipeline Partners - a stock they had owned for years, but no longer hold since 2007.
The Wells notice also concerns certain filings that the SEC staff claims were not made on time, Cooperman said in the letter.
In March 2015, Omega was subpoenaed by federal prosecutors and regulators seeking information about its trading activities in certain securities.
In the letter addressed to investors on Monday, Cooperman said the government investigations were ongoing and could be expanded.
"We believe we've done nothing wrong," Cooperman told CNBC.