In short: you cannot force customers to like your page and give out free wi-fi instead. But you can redirect users to your facebook page where they have the option to like OR you can use checkins/wallposts which has the same promotional value.
Facebook banned “Like Gates” after 30th of April, 2015. Here’s a brief statement / policy of this change, written by Facebook:
“You must not incentivize people to use social plugins or to like a Page. This includes offering rewards, or gating apps or app content based on whether or not a person has liked a Page. It remains acceptable to incentivize people to login to your app, checkin at a place or enter a promotion on your app’s Page. To ensure quality connections and help businesses reach the people who matter to them, we want people to like Pages because they want to connect and hear from the business, not because of artificial incentives. We believe this update will benefit people and advertisers alike.”
Basically Facebook wants users to like brand pages because they actually “like” them, not because they were promised some freebie or contest entry for doing it.
What this means is that you cannot force them to LIKE your page before you give them free Wi-Fi. However you can still ask them to LIKE your page after you gave them access to the hotspot. Therefore the LIKE button is displayed upon successful login. You can also redirect users to the venue's facebook page after they have logged in.
We recommend to use Checkins/Wallposts as your audience will grow the same way. More check-ins and engagement with your Page will also improve how it ranks in search.