From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
The Writers Guild of America strike resulted in the suspended production of the Re-imagined Series's fourth season, along with the majority of scripted US TV and film. The strike began on 5 November 2007, by which time the scripts of 11 episodes of Season 4 had been completed. Production finished shooting episode 11 in early December, and post production went on hiatus 28 February 2008.
There was widespread support for the strike among cast, crew and fans. Show-runner Ron D. Moore's personal blog kept a track on various strike-related activities including the "Pencils2MediaMoguls" campaign.
According to comments made by Ronald Moore to the 2008 San Diego Comic Con and included on the Season 4.0 DVD release, the episode "Revelations" may have served as the final episode of the series had the strike been prolonged enough to prevent a resumption of production. However Katee Sackhoff started that it would have been "Sometimes a Great Notion" that would have ended the series had the strike continued.
On February 13th, the writers voted to end the strike after 100 days. 92.5% of the votes cast were in favor of accepting the settlement with the studios .
Production resumed in late March, with the second half of Season 4 (dubbed Season 4.5) commencing broadcast in the United States in early 2009.