The Times reported that when she was asked for more detail about her position, Biggert said she was worried about what gay marriage would mean for "estate planning and other legal issues."
Biggert added that "we don't have polygamy and bigamy in the federal government. It's the states that take care of that."
She later clarified that statement by saying her point is that states deal with these issues, not the federal government.
Biggert this week announced that she received the endorsement of the Log Cabin Republicans.
"I'm thrilled to have the endorsement of the Log Cabin Republicans, a group that shares my commitment to an inclusive, big-tent GOP," she said. "Together, we can work toward a smaller, smarter federal government that respects the rights and privacy of all Americans."
Biggert also received a $500,000 donation from the American Unity PAC, which supports marriage equality. But other reports say some in the LGBT community are not happy that Biggert took this endorsement and is still just "close" to accepting gay marriage.