Kevin Muldoon, a former Newport Beach mayor and current city councilman there, claims Newsom's draconian order to close OC beaches -- from Newport Beach and Huntington Beach to Dana Point and San Clemente -- is a clear violation of their constitutional rights to freedom of travel, freedom of assembly and due process ... this according to docs obtained by TMZ.

In docs, Muldoon claims pictures from last month showing packed beaches in the OC that almost immediately triggered beach closures are incredibly misleading. He claims the photos were "taken from a ground level viewpoint, using zoom lenses that artificially compress perspective, seemingly showed beachgoers tightly packed together on Newport Beach."

He claims there are aerial pics that show far more space between beachgoers than the pics in the newspaper implied. What's more ... Muldoon claims it's completely unfair to single out the OC, which he claims has fewer COVID-19 cases than other places that did NOT have their beaches shut down. He claims other cities with closed beaches actually have more COVID cases.

Muldoon, who is suing as an individual and NOT in his official capacity as a councilman, claims sunlight and open-air reduce the likelihood of COVID transmission. It should be noted ... OC beach cities and individuals reportedly sued Newsom on Friday over his beach closures but a judge denied their request to nullify Newsom's order.

As we reported ... tons of pissed off residents flooded downtown Huntington Beach to protest the beach closures. There was also a plane flying a banner over the weekend that read "Fire Gruesome Newsom! Open California!"

Muldoon's asking a judge to declare the gov's order unconstitutional and prohibit its enforcement so peeps can enjoy the beach.