One of the most heavily used features of Facebook has got the social network in a bit of legal trouble.

It's being sued by the company that holds a patent for the "like" button — a patent that was granted in 1998, five years before Facebook came on the scene.

The man who patented the button, Joannes Jozef Everardus van Der Meer, is now dead — but Rembrandt Social Media has filed suit on his behalf.

It says Facebook is using the "like" button without permission.

Van Der Meer patented the button for a social network called Surfbook — a social diary that let people share information with friends and family.

Facebook says it has no comment.