AceShowbiz - Country rocker Jason Isbell is standing by his pledge not to play venues where he could be assured every audience member was vaccinated against COVID by pulling out of the Bristol Rhythm & Roots Reunion.

Organisers of the upcoming event on the border of Tennessee and Virginia revealed they would not be requiring proof of vaccination or a negative COVID test for entry, prompting Isbell to withdraw.

"We won't be appearing at the Rhythm and Roots Reunion this year," he wrote on Twitter shortly after festival bosses released a statement. "Y'all be safe!"

Two other headliners set for the event on 10-12 September - Tanya Tucker and Blackberry Smoke - are still hoping to perform, although Tucker recently cancelled all her August shows as she recovers from hip surgery, and Blackberry Smoke had to cancel concerts after guitarist Paul Jackson tested positive for COVID-19.

A spokesperson for the festival told Rolling Stone, "As it stands, Bristol Rhythm & Roots is prohibited from enacting a vaccination/negative test policy per Tennessee law. As a public event that utilizes multiple downtown businesses and vendors rather than a private venue/site, the stipulations surrounding our event protocols are unique."

But organisers have encouraged ticket holders who aren't vaccinated to "consider being tested prior" to the Reunion.

Jason Isbell also called off his scheduled gig on August 11 in Houston after the venue refused to comply with the health protocols he required.