The state would split from a new Internal Revenue Service policy recognizing same-sex marriage for tax purposes if the measure becomes law.
The proposal was added Monday night and is up for a Tuesday vote in the Senate.
Indiana Equality Action says the last-minute push could pose issues for couples who have a little more than a month to file taxes. The group also opposed a proposed constitutional gay marriage ban that was derailed earlier this session.
If passed into law, the Indiana bill would prevent same-sex couples from receiving the same tax breaks other couples now receive.
Republican Sen. Brandt Hershman of Buck Creek says tax policy is not the place to debate a social issue.
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