Shareholders of Fannie Mae and Freddie Mac got a mixed reception at the U.S. Supreme Court on a lawsuit that seeks billions of dollars and could affect the push to end government control of the mortgage giants.

Hearing arguments by phone Wednesday, the justices considered whether investors can challenge the 2012 agreements that let the federal government collect more than $300 billion in profits from Fannie and Freddie. A ruling in the investors’ favor in the case would give them a chance to collect a massive settlement.

Most of the justices directed tough questions at lawyers for both sides. Chief Justice John Roberts asked a government lawyer to respond to the investors’ contention that “their stock was completely wiped out in a unique way.” But later Roberts told a lawyer for the investors that “this was a lifeline thrown to your client.”

Common shares of both pared an early surge of about 20%, with Fannie Mae about 5% percent higher and Freddie Mac climbing some 9% in late morning trading.