"We're not quite satisfied," Mason said during a news conference at Los Angeles City Hall.
The comments came minutes after Commissioner
Sacramento mayor and former NBA great
"As soon as [NBA owners] can do it," Johnson said of a timetable to end Sterling's ownership.
Mason said players had been prepared to boycott playoff games if Silver didn't issue a severe punishment.
The news conference appeared to mark a turning point in the often-contentious relationship between the NBA and union. Johnson described Silver as the "players' commissioner" and praised his swift action against what Johnson called a "rotten apple" and "cancer."
Ron Klempner, acting director of the players' union, said Tuesday was a "transcendent" moment for the league and that he believed the ownership vote would be resolved as quickly as possible.