Mary Cheney, the lesbian daughter of former US vice-president Dick Cheney, has condemned her older sister, a Republican who is running for the Senate, for her opposition to same-sex marriage.

In a statement on Friday, Liz Cheney said that she was “not pro-gay marriage.”

She said: “I am strongly pro-life and I am not pro-gay marriage. I believe the issue of marriage must be decided by the states, and by the people in the states, not by judges and not even by legislators, but by the people themselves.”

According to the New York Times, Mary Cheney wrote a message on Facebook responding to her sister’s views: “For the record, I love my sister, but she is dead wrong on the issue of marriage.”

“Freedom means freedom for everyone,” she said, repeating a phrase once used by her father when he was asked about same-sex marriage. “That means all families – regardless of how they look or how they are made — all families are entitled to the same rights, privileges and protections as every other.”

She added that the issue of marriage was “not something to be decided by a show of hands.”

Dick Cheney, who served as vice president under President George Bush, has long shown his support for same-sex unions, saying that “people should be free to enter into any kind of relationship they want to enter into.” He also agreed with his daughter Liz, however, that this should remain in the hands of voters.

Mary Cheney married her wife Heather Poe in June last year, and she so far given birth to two children.

She had her first baby, Samuel David, in 2007.

She then had her second baby, daughter Sarah Lynne Cheney, in 2009.

In defending her right to raise a child in a same-sex relationship, Mary Cheney said: “This is a baby. This is a blessing from God. It is not a political statement. It is not a prop to be used in a debate, on either side of a political issue. It is my child.”