On August 7, 2014, Facebook announced that they have changed their platform policies so brands can no longer incentivize users to like a Page;
In layman’s terms, you cannot have applications that show one set of content to non-fans, and another set of content to fans.
For several years, fan-gating a sweepstakes (requiring a user to click the like button before the entry form is unlocked) has been an effective method of increasing new fans for a business. All existing applications will continue to work until November 5.