Marvin Gaye's Son -- You Can Bet We're Gonna Sue Over 'Blurred Lines'

Marvin Gaye's son is out for blood in his war with Robin Thicke, telling "TMZ Live" he resents Thicke's lawsuit against the Gaye estate over "Blurred Lines" ... and is strongly insinuating he plans to respond with legal action of his own.

Marvin Gaye III dropped us a line Wednesday, and he's not happy ... basically saying Thicke has disrespected the Gaye family by shamelessly lifting his father's famous tunes for the hit song (plus many other Thicke tracks).

As you know, Thicke has filed a lawsuit against the Gaye estate, asking a judge to head off any legal action from the Gayes by ruling "Blurred Lines" does NOT violate Marvin's copyrights.

Marvin III says Thicke's lawsuit is a total slap in the face.

Marvin III hedged when we asked flat out if he plans to sue Thicke for copyright infringement ... but the message was clear.