The organisation is campaigning for marriage equality in the states of Maine, Maryland, Minnesota and Washington.
"It's unbelievable to me that people's lives and relationships are literally being voted on in a matter of days," wrote the Benjamin Button star (pictured at the Sundance Film festival) in an email to HRC members and supporters on Wednesday. "If you're like me, you don't want to have to ask yourself on the day after the election, what else could I have done?"
Brad famously said that he and Angelina Jolie would not wed until everyone in the US was legally allowed to tie the knot. But pressure from their six children made the couple change their minds. The announced their engagement in April with a statement from the couple's spokesperson. "Yes, it's confirmed," Brad's manager Cynthia Pett-Dante told People. "It is a promise for the future and their kids are very happy. There’s no date set at this time."
"We'd actually like to (get married), and it seems to mean more and more to our kids," Brad told The Hollywood Reporter just before presenting his leading lady with a flawless diamond ring that was a year in the making.
"We made this declaration some time ago that we weren't going to do it until everyone can. But I don't think we'll be able to hold out." There's been widespread speculation as to when the couple will wed, but numerous stories over the summer that a wedding was imminent turned out not to be true. The couple say there is still no date on the horizon. Brad said at a recent screening: "No plans yet. Other than, we're gonna do it."
He has also revealed that close pal George Clooney probably won't be taking on best man duties, saying: "George doesn't like institutions. Perhaps he could show people to their seats."
For the moment, the family are busying themselves with Halloween. Angelina recently dropped into Party City in Sherman Oaks to pick up supplies and costumes for the family.
According to website RadarOnline.com, store manager Mauricio Salazar revealed Angelina had bought a Morticia Addams costume for herself and a Texas Chainsaw Massacre Leatherface costume for her fiancé.
"She also bought a bunch of outfits for the kids. A Robin costume, a Beaker the Scientist costume, a pony and a vampire costume. Angelina also bought fake insects and creepy crawlies, make-up and decorations."