From the New York Times [Emphasis mine]:

The chief executives of the nine largest banks in the United States trooped into a gilded conference room at the Treasury Department at 3 p.m. Monday. To their astonishment, they were each handed a one-page document that said they agreed to sell shares to the government, then Treasury Secretary Henry M. Paulson Jr. said they must sign it before they left.

[...]“It was a take it or take it offer,” said one person who was briefed on the meeting, speaking on condition of anonymity because the discussions were private.