The hierarchy of the Roman Catholic Church in the United States has donated $200,000 (£124,000) to the campaign to ban gay marriage in California.

Voters in America’s most populous state will decide on Proposition 8 on election day next Tuesday.

Campaign finance records show the US Conference of Catholic Bishops made the donation to ProtectMarriage.com, the coalition that gathered more than a million signatures to get Proposition 8 on the ballot.

While Mormons and evangelical Protestants have also made sizable monetary contributions, the single largest donor is The Knights of Columbus, a Roman Catholic fraternal organisation, which gave $1.4m.

An estimated $60m has been donated on both sides – Hollywood stars such as Steven Spielberg and Brad Pitt have donated large sums to the campaign opposing Prop 8 and the Screen Actors Guild has voted to officially oppose the California ballot initiative.

The most recent Field Poll found 49% of likely voters oppose Proposition 8 and 44% support it, with 7% undecided.

Proposition 8 would amend the state Constitution to “eliminate right of same-sex couples to marry.”

In May the California Supreme Court overturned a ban on same-sex marriages in the state.

The Court voted 4 to 3 to strike down the ban, ruling that lesbian and gay couples are entitled to the same fundamental right to marry as heterosexual couples as protected by the California constitution.

The decision explicitly struck down Proposition 22, a voter-passed initiative in 2000 that sought to limit marriage to between a man and woman.

Days later Pope Benedict XVI, speaking in Rome to representatives of family organisations, did not refer to the court ruling but in comments widely interpreted as restating the Roman Catholic position he said:

“The union of love, based on matrimony between a man and a woman, which makes up the family, represents a good for all society that can not be substituted by, confused with, or compared to other types of unions.”

“Prop 8 trailed in The Field Poll’s initial measurement in July by nine points (51% No to 42% Yes) taken shortly after it qualified for the ballot,” according to today’s Field Research Corporation poll of 966 likely voters in California.

“The No-side advantage increased to fourteen points (52% to 38%) in September, when voters were asked to react to its original ballot description, which referred to the measure as the “Limit on Marriage” initiative.

“However, following the state Supreme Court’s ruling that the state’s existing same-sex marriage ban was unconstitutional, thereby making it legal for same-sex couples to marry in California, state Attorney General Jerry Brown changed Prop 8’s official ballot title to the “Eliminates Right of Same-Sex Couples to Marry” initiative.

“When voters were read this amended description in September, the No-side lead grew to seventeen points (55% No vs. 38% Yes).

“Now, after more than a month of intensive campaigning on both sides, the initiative trails by just five points, 49% No vs. 44% Yes, with 7% undecided. Yes-side support has increased six points, and those opposed declining six points over the past month.”

On Wednesday the state’s Governor, Arnold Schwarzenegger, said he would be voting no on Prop 8. His wife Maria Shriver said earlier this week:

“I believe in people’s right to choose a partner that they love, and that’s a decision that I have come to, and I have felt that way for a long time.”

Computer giant Apple has declared Prop 8 a civil rights issue and donated $100,000 to the campaign to defeat it.

Google has also publicly backed gay marriage.