Mural Art clearance for Union Indie Feature

Recently rented my space as a shoot location to an indie feature. We were ensured none of the artwork in our space would appear on camera, thanks to set dressing/art dept. However, the mural in our space was prominently featured on camera. The mural was not in their contract, or part of our agreement and the producers lied profusely about the overall scale of this production to get a better rate from us on location fee. What is a fair and industry standard rate for mural artwork release for a Union independent feature film? THANK YOU ARTCUBE NATION