Hollywood star Brad Pitt has agreed to donate $100,000 (£62,000) to help the Human Rights Campaign raise money for its efforts to support equal marriage initiatives in several US states.

America’s largest LGBT rights organisation announced on Wednesday that Pitt had agreed to match contributions from the group’s members by up to $100,000.

In an e-mail to members of the Human Rights Campaign, Pitt wrote that it’s “unbelievable” that people’s relationships will be put to a vote on Election Day.

Same-sex marriage will be on the ballot in Maryland, Maine, Minnesota and Washington state.

The Human Rights Campaign says it has spent $8 million (£4.97 million) to push for marriage equality over the past two years, including $5 million (£3.1 million) in the four ballot measures this year.

Last week, New York Mayor Michael Bloomberg offered $500,000 (£312,000) from his personal fortune towards the push for marriage equality in Maine, Minnesota and Washington.

In September, Brad Pitt endorsed President Obama’s re-election campaign and said that marriage equality was “inevitable”.

Pitt’s mother, who opposes the measure, has already announced her support for Republican candidate Mitt Romney.