The social media giant tested out the ability to "downvote" posts on its site in the US in February, and they are now carrying out further research into the feature in New Zealand, with a second trial of the button which appears on some public posts.
According to BBC News, there are no immediate plans to roll it out across the social network, but further testing could make the option more likely to appear on the site as a whole.
The concept came about after discussion site Reddit has had longstanding success with its ability to "upvote" popular posts and "downvote" unpopular ones, with the greater number of downvotes reducing the visibility of that particular post.
It would mean that negative comments and the spreading of hate across the internet could be lowered, as downvoted comments wouldn't get the same amount of visibility as they do currently.
Facebook said the button was being tested to see whether it enabled "better public discussions".
A spokesperson added to BBC News: "Our hope is that this feature will make it easier for us to create such spaces, by ranking the comments that readers believe deserve to rank highest, rather than the comments that get the strongest emotional reaction."
Currently, users have the option to "like" a post or comment, or leave a "reaction" - such as happy, sad, or angry - in the form of a small emoji beside the post.
However, Facebook have insisted that the trialled feature is not a "dislike" button, and won't work in the same way that the "like" feature does.
Jack Kent, an analyst at IHS Markit, told BBC News: "Given the current debate about Facebook's role in public online discourse and news, it makes sense that the platform is trialling different ways for users to interact with content in a public setting.
"While the company has been quite vocal in its opposition to launching a 'dislike' feature, it did expand its options from simply liking posts and content to a range of emojis in 2016."