Depends on the synod.
The LCMS and WELS are the two big synods that forbid it ( I am LCMS), and there are a lot of smaller ones that do to.
The ELCA can't make up its mind if it is a Christian denomination or a debate society, so they don't have many rules on forbidding anything.
Thanks for the info, I googled the subject myself and by chance found the website of a Lutheran Church in New York that apparently has an on going debate over allowing the Boy Scouts to meet in their church fellowship hall. The page on the website made reference to the fact that many of our American founding fathers were Masons, and opined, something to the effect, "Is the God of our founding fathers, one nation under God, a false God". The website of this particular church apparently thought not.
http://www.stpeter-brooklyn.org/serious_problem.html
I noted that the Lutheran objections to masonry are generally based on bad rumors, oft-reported as truth, most of which debunked in this thread.
One particular struck me as funny: objection that the lamb-skin apron was a statement that salvation could be earned.
The lamb skin apron is actually symbol of Christ, the paschal (passover) lamb, who covers us with GRACE given freely to us, NOT earned, and by that GRACE and not acts salvation is obtained.