Well, a lot depends on how far you take it. Mike says this other artist has been quite blatant about it, to the extent of even copying from Mike’s books and exhibition catalogues. And sadly, some of the more unscrupulous gallery owners who sell Mike’s works, are happily showing and selling this other artist's paintings – I presume because they are cheaper – despite knowing full well that they are so similar to Mike’s work that they could be mistaken for his work... certainly to the untutored eye of a potential customer. Mike has tried to ignore it over the years, hoping that the man would eventually develop his own style and ideas. Unfortunately, this has not been the case. If Mike changes his subject matter, to try something new - so does this other chap, he behaves like a "stalker", to quote Mike. The important point is...........it is clearly now having quite a severe impact on Mike's peace of mind AND his sales.
This is NOT the same as copying the style of a master from the past, who cannot be directly affected. If a living artist copies the style, or work of another living artist, and as a result affects that artist's livelihood, that is simply out of order.