Stephen Crabb has announced his bid for the Tory leadership under the slogan "a plan for unity and opportunity".
But some people are questioning his credentials on unity, saying his views on homosexuality mean he shouldn't be the next Tory leader and Prime Minister.
In 2013 Crabb voted against gay marriage, and in 2007 he voted against the Equality Act (Sexual Orientation) Regulations which outlawed discrimination on the grounds of sexual orientation.
Crabb defended his decision to vote against gay marriage at the time, saying he voted in line with his Christian faith.
The Guardian says Crabb was a parliamentary intern for the Christian group Care, and has since taken interns from the organisation to work with him. The organisation is opposed to same-sex marriage.
Crabb said his views were not relevant to the leadership campaign.
He said: "We had that debate in the last Parliament about gay marriage. I voted the way I did but I'm very happy with the outcome that issue is now settled, we move on from it."