Tepper has been at odds with TerraForm Power, a so-called yieldco formed by SunEdison, over a plan to buy some residential solar power assets from SunEdison. He previously sent a letter to TerraForm Power's board questioning the deal.
In an SEC filing Wednesday, Tepper raised the stakes.
"The Reporting Persons are independently exploring potential claims of impropriety against the parties (including their respective advisors) concerning the Issuer's and SUNE's transactions described herein," Tepper said of the dealings between TerraForm Power and SunEdision.
TerraForm Power shares fell 2.5 percent in morning trading, while SunEdison shares rose 1.8 percent.
This story is developing. Please check back for further updates.
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—Reuters contributed to this report.