Opponents say the ban is unnecessary because Indiana law already defines marriage as between a man and a woman, and they contend putting it in the constitution will paint Indiana as an unfriendly state and stifle efforts to attract top talent.
Supporters argue the ban should be placed in the constitution to make it more difficult for future lawmakers to reverse.
DePauw and Wabash, both private colleges, join Indiana University and top businesses including Eli Lilly and Cummins Inc. in their opposition. Purdue University officials say the school, led by former Gov. Mitch Daniels, will not take a position on the issue.
"Our students come from around the country and around the world, and our fundamental goal is to educate them to think critically, exercise responsible leadership, communicate effectively, and tackle complex problems. This depends on attracting talented faculty and staff, a task that is made more difficult by the passage of this amendment," DePauw President Brian W. Casey and Wabash President Gregory D. Hess said in a joint statement.
State lawmakers have passed the amendment once. It must pass again in the session that begins in January in order to go before voters next November.