Thicke, his producer Pharrell Williams and collaborator T.I. filed a pre-emptive suit in August (13), asking a Los Angeles judge to declare that Blurred Lines does not infringe on Gaye's 1977 song, after the late legend's heirs first expressed copyright concerns.
The trio faced similar claims from Bridgeport Music bosses, who own the rights to George Clinton's band Funkadelic's compositions - they alleged the tune bears striking similarities to Funkadelic's track Sexy Ways.
Thicke recently confessed he was eager to reach a settlement to avoid a drawn out court battle with his idol's relatives, but they reportedly rejected a six-figure sum, and now Nona and Frankie Christian Gaye have lodged a countersuit in a California court to pursue their claims.
In court papers obtained by editors at The Hollywood Reporter, the Gayes point to interviews conducted by both Thicke and Williams, who have openly admitted that the singer used Got To Give It Up as the inspiration for Blurred Lines.
They have also consulted expert musicologist Judith Finell to compare the two songs, and she has stated that she found "at least eight substantially similar compositional features" in the two tracks, "far surpassing the similarities that might result from attempts to evoke an 'era' of music or a shared genre".
The Gayes go on to suggest that Thicke has lifted material from their tragic father for years, listing a second copyright infringement regarding the star's 2011 tune Love After War, which they believe is modelled on the late soul star's After the Dance.
They are demanding damages, including a cut of profits from both songs.
In their new legal papers, filed on Wednesday (30Oct13), the Gayes also argue that Thicke's song Make U Love Me features "a similar bridge and identical lyrics from Marvin Gaye’s I Want You."