Ballard on Friday signed a resolution against the measure, joining a group of businesses, universities and others who say the amendment would keep workers and businesses from moving to Indiana.
Social conservative organizations have begun coordinating in support of the measure, which they say is needed to keep courts from potentially legalizing gay marriage.
Indiana already limits marriage to being between one man and one woman. Indiana lawmakers are set to consider amending that definition into the state constitution during the upcoming session.
If successful, the measure would then be placed on the ballot for consideration by voters next November.
A former Ballard campaign manager leads the campaign against the marriage amendment.
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