Olivia Dean's got a copyright fight swirling around one of her songs ... with Bill Withers' publisher claiming her track sounds a little too much like his timeless classic, "Just the Two of Us."

According to a new lawsuit, obtained by TMZ, Mattie Music Group -- which says it owns rights to the Withers classic -- is suing Capitol Records, Universal Music Group, Sony Publishing and Kobalt Music Publishing for copyright infringement.

The song at the center of it all is Olivia's "I've Seen It." The publisher claims her track copied significant portions of "Just the Two of Us" -- specifically, its distinctive melody.

Mattie says it even brought in a musicologist, who the suit says found substantial similarities between the two songs.

The publisher also points out "Just the Two of Us" was a huge hit -- reaching No. 2 on the Billboard Hot 100 and winning a Grammy -- arguing Olivia and her cowriters had plenty of opportunity to hear it.

Worth noting ... Olivia herself is NOT named as a defendant.

The publisher says it warned the labels in August, but claims they kept distributing and licensing the track anyway. Now it wants damages, profits tied to the song, and an order stopping further alleged infringement.

We've reached out to Olivia's reps for comment ... so far, no word back.