GW did indeed go after people for using the term "space marines." The EFF helped defend the targeted author, and got the book put back on Amazon.

A few years before that, they went after John Wick for his use of "orks" in his FRPG "Orkworld;" John, lacking the EFF's resources, wound up just pointing out that his orks were standard high fantasy goblinesque people with nothing to do with spacecraft or an SF setting.