Despite boasting support from 600 corporations, the Equality Campaign has not received any big donations from Australian companies to prosecute the yes case in the same-sex marriage postal survey.

The Qantas chief executive, Alan Joyce, has promised to make a significant personal donation and some companies, such as Airbnb, have run their own campaigns to promote marriage equality but neither the Equality Campaign nor Australian Marriage Equality has received any big corporate donations over the last two years.

I will spend as much time as the campaign wants me to speak about this Alan Joyce

Even major partners of the Sydney Gay and Lesbian Mardi Gras, such as ANZ, Ansell, Holden and Medibank, reiterated support for marriage equality when contacted by Guardian Australia but conceded they had not made a donation.

The Equality Campaign insists it has no complaint that corporate Australia has kept its purse strings tight because it plans to run a people-powered campaign. However, opponents have been quick to paint same-sex marriage as an elitist issue, in part, because of the extent of corporate support.

The Australian Marriage Equality co-chair Alex Greenwich said: “We will be massively outspent by the unlimited buckets of cash that opponents of equality have access to.”

Greenwich said that if the postal surveywent ahead, the Equality Campaign “needs to fundraise and [is] grateful for the support we have received from grass-roots supporters, community groups, local councils, and LGBTI employee networks”.

The 600 corporate supporters of Australian Marriage Equality have signed an open letter in support of same-sex marriage.

“We support the right for all our employees to have equal opportunities in life. We therefore support marriage equality,” the statement says.

It also makes the argument that marriage equality is “a sound economic option” contributing to a happy, productive workforce and attracting global talent to Australia. “Equality in the workplace works; Discrimination does not.”

A spokesman for Holden said: “Holden’s support for equality in all its forms is well known. While not financially active in this particular campaign, Holden has been a public supporter of marriage equality for some time now.

“It’s important that Australians have the opportunity to have their say on this issue.”

A spokesman for ANZ said the bank “continues to support marriage equality and has always been an advocate of diversity and inclusion”.

“We are encouraging employees to have their say and to do so in a thoughtful way. How they vote is a personal matter for them,” he said.

A spokeswoman for Medibank said the health insurer “believes that every person should enjoy equal rights, and that includes marriage”.

“Medibank has not made a corporate donation to the Equality Campaign.”

She said Medibank would match donations made by employees to “any registered charity”, including those supporting the marriage equality campaign. However, charities on the no side – such as the Australian Christian Lobby – also qualify.

A spokesman for Ansell said it supported marriage equality and its sexual wellness unit, which has campaigned encouraging enrolment, would decide whether to issue a further statement after a high court challenge to the postal survey is heard.

The country manager of Airbnb in Australia, Sam McDonagh, said it “strongly believes that everyone should have the right to marry the person they love”.

“At Airbnb we champion diversity, inclusion and the need for equality in many forms right around the world. In Australia, one of the most important examples is the support we are throwing behind the issue of marriage equality,” he said.

McDonagh labelled the postal survey “an unnecessary, lengthy and costly path to achieving equality in Australia” but said the company had thrown its “full support behind Australian Marriage Equality and the yes campaign”.

“We’ve been thrilled by the overwhelming response from Australians to the Until We All Belong movement, with more than 150,000 people proudly wearing acceptance rings and pledging their support on behalf of friends, family members or loved ones with strong support even coming from within the corridors of parliament.”

Last Friday, Joyce said he would “personally donate a significant amount of money to the campaign”. “I will spend as much time as the campaign wants me to speak about this,” he said.

Joyce, who was attacked with a pie in May by a Perth man because of his outspoken support for same-sex marriage, has been an advocate of companies taking a public stance on social issues in the same way they do for policy issues such as company tax, industrial relations and trade.

On Tuesday, the Coalition for Marriage launched its campaign with a TV ad linking same-sex marriage to gender education.

In similar comments to Radio National on Thursday, the Nationals senator Matt Canavan told Radio National Australians should listen to “mums and dads who are concerned about what their kids are taught in the classroom” rather than “ministers, big businesses, [and] big unions”.

The Marriage Alliance spokeswoman Sophie York, in an email calling on supporters for donations, said the no campaign “may not have the resources of our opponents, or the support of much of the mainstream media”.