Sandra Denton -- aka Pepa from Salt-N-Pepa -- is suing the ride-share service along with one of its drivers and the drivers of 3 other vehicles, claiming a 2018 chain-reaction car crash left her with injuries, pain, and loss of wages.

In docs, obtained by TMZ, Pepa claims the crash on L.A.'s 101 freeway was triggered after the Uber driver and other drivers "operated their vehicle negligently and carelessly."

Pep's suing for damages including loss of wages. Sources close to the situation tell TMZ ... the rapper was in an Uber that was involved in an accident. Cops say another Uber driver was following too closely behind, couldn't stop in time ... and hit another ride, causing a chain reaction.

We're told Pepa complained of neck and knee pain, for which she later needed medical attention. As a result of the accident, sources say the Grammy winner still suffers intense pain that interferes with her performances and travel, often making herself sick during and after stage performances.

We've reached out to Uber, so far no word back.