The Senate Judiciary Committee advanced the amendment on a 7-3 party line vote Wednesday, with Republican senators rejecting arguments that language prohibiting civil unions could threaten the ability of employers to offer domestic partner benefits.
Amendment sponsor Sen. Dennis Kruse of Auburn says the measure isn't meant to affect any benefits offered by companies and he doesn't believe that it would.
Current state law bans gay marriage.
The Republican-led House approved the amendment last month before the Democratic boycott began. If the measure passes the Legislature this year, it must pass again in 2013 or 2014 to go before voters on the 2014 ballot.