Virginia Delegate Bob Marshall, a Republican from Prince William County, said this week that he would not refer to his opponent Danica Roem, a transgender woman, using female pronouns because she defies the “laws of nature” at a “fundamental level.”

Marshall, a vocal opponent of LGBT rights who is serving his 13th term, earlier this year introduced a bill that sought to prohibit transgender people from using the bathroom of their choice.

If elected on Tuesday, Roem, a journalist, would become the state's first openly transgender elected official. The Washington Post described the campaign as possibly Marshall's “toughest reelection battle.”

During an appearance Friday on Sandy Rios in the Morning, Marshall told host Sandy Rios that his opponent was living in a “fantasy.”

“It is not a civil right to masquerade your fantasies as reality,” Marshall said. “But standing up to this is somewhat difficult because you get called all kinds of names. And if you’re going to be shying away because someone calls you a bigot or a transphobe or whatever it is, it probably is not something that you should attempt.”

Marshall added that he intended to stand his ground.

“I’ve drawn a line. I’m not leaving it, because I don’t make the laws of nature but I think I understand them, at least at this fundamental level. I never flunked biology, so I’m not going to call a man a woman, period,” Marshall said.

Earlier this month, former Vice President Joe Biden endorsed Roem's campaign.

(Related: Social conservatives running anti-transgender robocalls against Danica Roem.)