A Christian MP's bill to ban gay marriage, due to have its first reading in Parliament this week, is just a sore loser's response to the success of civil unions, says Progressive MP Matt Robson. The Marriage (Gender Clarification) Amendment Bill is a private member's bill sponsored by United Future MP Larry Baldock, which will ban same-sex couples from marrying, and amend protections for gays contained in the Bill of Rights. Due to be voted on this week, Baldock told GayNZ.com his bill was needed because married heterosexuals needed to be clarified on what marriage meant. Matt Robson says that Baldock has difficulty understanding the current law. "The courts have already made in clear that marriage under current law means as between people of different gender," he says. "Whether that will remain the case as our understanding of human rights develops is a moot point. But what part of the present law doesn't Mr Baldock understand?" Both Progressive MPs will be voting against the bill. "This is just a sore loser's response to the passage of the Civil Union Act."