LGBT civil rights groups in Vermont are mounting a massive campaign to secure a veto-proof House vote on gay marriage.

The House is expected to vote later this week on a marriage equality bill. The measure passed the Senate last week with a massive 26-4 vote. It is expected to pass the House with a much narrower majority.

Following Senate passage of the bill, Gov. James Douglas (R) announced he would veto it.

Since then same-sex, marriage advocates have been stepping up the campaign to win enough House votes to override a veto.

On Friday, hundreds turned out at the Statehouse in a show of support. They buttonholed lawmakers and are using a telephone campaign to try and sway opponents and undecided representatives.

"No one said this would be easy," Senate President Pro Tem Peter Shumlin, D-Windham, told the rally. "But we are more determined than ever to overcome his veto."

Rep. David Zuckerman said the bill currently has more than 75 strong supporters in the House, but it would take 101 votes to overcome a veto.