Green Bay Mayor James Schmitt fired off an angry letter to NFL Commissioner Roger Goodell -- as promised -- claiming the labor dispute with referees is threatening the Packers on-field success ... AND putting the entire Wisconsin town in financial jeopardy.

TMZ obtained a copy of the letter ... in which the Mayor claims the NFL's elite status is being "threatened by less than qualified officials who are not quite at the same level as the rest of the league's representatives."

Mayor Schmitt, who's also a shareholder of the publicly owned Green Bay Packers, continues ... "last night's game creates a negative perception on the NFL brand, which in turn jeopardizes the Packers' chance for success as well as the potential to negatively affect our local economy."

All in all, it's a pretty polite way of saying it totally sucks that replacement refs cost Green Bay's greatest commodity -- the Packers -- a victory last night.

The Mayor of Green Bay is so pissed about last night's game -- where replacement refs ROBBED the Packers of a win -- he's going straight to the NFL's head honcho to demand the real refs get back on the job ... TMZ has learned.

Mayor James Schmitt tells TMZ he's drafting a letter to NFL commissioner Roger Goodell ... urging him to end the ref lockout because it's compromising the integrity of the NFL.

Exhibit A -- last night's refs robbing the Packers of a win by incorrectly calling Green Bay's interception in the endzone ...a touchdown for the Seattle Seahawks. The Pack lost 14-12.

Schmitt says, "This is not right. I understand talent costs money, but when it comes to the crucial role of the referees ... it has to be a top priority."

Hizzoner is in a unique position because he's also a shareholder in the Green Bay Packers -- the only NFL team publicly owned.

But the Mayor makes it clear ... "We are not protesting losing the game. We are protesting the quality of officiating."

Church.