Usher and Chris Brown got into a verbal argument last night, which delayed their Atlanta show by nearly three hours … and sources say issues between them remain unresolved. 

Sources close to the situation tell TMZ … there was a ton of traffic around the venue last night … which caused a lot of fans to be late. 

We’re told the issue caused tension backstage because Usher wanted the show to go on … while Chris wanted to wait for all the fans to arrive.

Our sources say the two singers went back and forth. A source said Usher and Chris have been extremely competitive the entire tour.

However, our sources say the tension reached a head last night due to “egos.” We’re told they do not believe the R&B Tour is in jeopardy, but the two have not worked out their problems. 

As TMZ previously reported, fans were furious after the duo played in Atlanta last night because the singers were super late. The two are set to perform in ATL tonight.