The new coalition, called Hoosiers Unite for Marriage, is made up of several groups in the state that are fighting for gay marriage.
Representatives Rebecca Kubacki and Kathy Heuer lost their seats to primary challengers on Tuesday.
Whether to amendment Indiana's constitution to define marriage as between a man and a woman was the main issue debated in the 2014 session.
The National Organization for Marriage wants to put HJR-3 on the ballot despite lawmakers passing a measure indicating it must be approved in 2015 or 2016.
The amendment's passage is the first step to putting HJR-3 on the ballot in 2016.
Political analysts say the measure has less of a chance for approval in 2016 than it would have if it were on the ballot this year.
The Senate plans to vote on the proposed marriage amendment Monday, but it will not be sent to the voters this year.
The Senate today did not reinsert the second sentence to the proposed constitutional amendment defining marriage as between a man and a woman.
A group of young adults gathered at the statehouse today to show their support for the proposed amendment defining marriage as between a man and a woman.
The full Senate will likely vote on the measure this week.