Florida Georgia Line -- Backstage Cop Trouble ... Police Pull Escort Detail

Florida Georgia Line dissed law enforcement working security at their concert ... according to an Iowa Sheriff who says the band banned officers, and then came crawling back for protection.

Jones County Sheriff Greg Graver tells TMZ he was headed backstage Saturday night at the Great Jones County Fair to discuss security protocol with the band when he was stopped by a crew member and told no uniformed officers were allowed backstage, per the band.

Sheriff Graver says he was told the country duo even threatened to pull the plug on the concert if they saw any cops.

Graver says midway through the performance, he was told the band wanted a police escort out of town after the show -- but he told them he wouldn't spend "one tax dollar assisting them" ... after being disrespected.

He says the band's management scrambled for other law enforcement agencies to provide the escort ... but they also told FGL to kick rocks. They ended up leaving on their own.

A similar incident went down with Wisconsin cops last week. We've reached out to the band ... no word back.