If you follow or like a Page on Facebook, and another Page tags that page on Facebook within their own post, there's a higher likelihood that you'll see that post in your feed, even though you haven't liked or followed that brand or business.
Here's the example Facebook provided, in which Bleacher Report's Facebook Page tagged Dwight Howard's Facebook Page:
This announcement follows on the new trending feature Facebook launched in January. Like Facebook's Trending topics, the Page tagging update will allow users to see content they are expressly interested in, while introducing them to new sources of information about those topics and potentially find new Pages to like.
However, one significant downside to this feature is that spammers could potentially start tagging popular Pages within their own posts, in the hopes of showing up on the news feeds of Facebook users they otherwise couldn't reach.
The only way to really compensate for this would be for people to report the post as spam, but it might not be spam in the most direct sense. You could potentially require the tagged person or page to approve it first, but in a fast moving social site, that approval might not happen for hours or days – if at all, especially for pages and people that aren't that active.
For example, if you like the Vancouver Canucks on Facebook, and a spammer has an affiliate hockey ticket site or hockey jersey site, they could tag the Vancouver Canucks Facebook Page in their posts in the hopes that people who have liked the Canucks will see that post and possibly buy from their affiliate link or website, especially if they coincide it with a like/share/click campaign as well to artificially inflate its popularity. So this could quickly become spam central on Facebook.
Facebook says that is working to ensure that only the most relevant stories appear in news feed from these related pages. One of the criteria it seems to be following is looking at ones that have the most engagement such as likes, comments, shares, and clicks. This could possibly help the spam issue, although it also opens up the possibility of those spam pages with their spam Facebook posts being inflated with something like buying Facebook likes in order to increase the odds it appears in others newsfeeds feeds.