The film will be about the Chicago Seven, a group of anti-war protesters in 1968 who were tried for inciting a riot at the Democratic National Convention. Some of it would have been based on a documentary that comes out in limited release this Friday called Chicago 10.
It was supposed to start filming in April, but that is too close to the strike deadline for the Screen Actors Guild contract which could decide to go on strike 2 months later.
This releases any potential cast members to do other projects before the strike deadline while the script and production are sorted out.
Will Smith, Philip Seymour Hoffman, Jeff Daniels, and Kevin Spacey have all been rumored as members of the cast. But at this time anything you read or hear about them being a part of the project officially is a dirty lie. The only person officially part of the group is Sacha Baron Cohen as Abbie Hoffman.
This delay is not necessarily a bad thing. He isn’t out of it completely like Collider originally reported. He’s just delaying it (according to Nikki Finke) and instead shifting his focus to the original plan after Indy 4. which was to work on Lincoln starring Liam Neeson.