The socially conservative Republican said the proposed protection represents a "disturbing trend" of the incremental erosion of heterosexual marriage. Rhode Island does not recognize same-sex marriage.
"If the General Assembly believes it would like to address the issue of domestic partnership, it should place the issue on the ballot and let the people of the State of Rhode Island decide," Carcieri said in a letter to lawmakers.
Democrats hold a veto-proof majority in the Legislature and frequently override Carcieri's objections.
Sen. Rhoda Perry and Rep. David Segal, the bill sponsors, said they would seek to override the veto. They proposed the legislation after one of their constituents was unable to retrieve the body of his late partner from the state medical examiner for weeks because they weren't married or next-of-kin.
Gay rights supporters were indignant at the veto.
"It is absolutely unconscionable that Gov. Carcieri would step in the middle of people being able to take care of their loved ones at such a sorrowful time," said Kathy Kushnir, executive director of Marriage Equality Rhode Island, which advocates for gay marriage. "Why would he make it more difficult? I just don't get it."
The proposed funeral planning rights would apply to same-sex couples who have had a relationship for at least one year and pass other tests, such as owning property together. Carcieri said some of the guidelines were vague.