The Catholic church in Sydney has sent letters to at least two companies that publicly support same-sex marriage, to express its “grave concern” and accuse them of “overstepping their purpose”.

The companies said the letter did not change their stance on same-sex marriage.

Guardian Australia has seen the letter addressed to Steve Walsh, the chairman of law firm Maurice Blackburn, sent by the business manager of the Catholic Archdiocese of Sydney, Michael Digges.

In the letter, Digges writes the church is a “significant user of goods and services from many corporations, both local and international” and reminds the firm that many of its “employees, customers, partners, suppliers” would belong to the Catholic faith.

“You are publicly supporting a strategic, political and well-funded campaign designed to pressure the federal government into changing the Marriage Act,” he writes.

“I wonder whether you have questioned whether it is the role of a corporation such as yours to be participating in such an ­important matter that impacts all of Australian society now and into the future.

“For corporations to speak on such issues on behalf of shareholders, employees, clients/customers, suppliers and other stakeholders is indeed overstepping their purpose and is to be strongly resisted.”

An open letter of support posted on the website of advocacy group Australian Marriage Equality (AME) features more than 180 signatories from across the corporate world, include Australia’s big four banks, McDonald’s, KPMG, Qantas, Twitter, Telstra and Airbnb.

AME’s deputy director, Ivan Hinton-Teoh, told Guardian Australia it was “ironic” a religious institution would consider a corporation’s views on civil law as “overreach” and said with 72% of Australian now marrying outside the church, “reform to the Marriage Act is reform to a civil institution”.

He said they had not received any negative feedback from their corporate partners due to the church’s letter. Instead, more corporations, including the Greater Building Society, had joined the campaign and it was clear the church’s most recent action “will not have an effect”.

The Greater Building Society’s chief executive, Scott Morgan, said it was “thrilled” to be joining corporate support for equal rights for all Australians. “At the Greater, we believe wholeheartedly that our diversity gives us strength. We want all of our employees and customers to enjoy the same basic rights.”

Hinton-Teoh said these organisations “would have considered what the community response was going to be to their support of marriage equality”.

“And it shows very clearly these corporations are acutely aware that the majority of Australians are now impatient for reform.”



A 2014 survey by Crosby Textor found that 67% of respondents who belonged to the Catholic faith strongly supported same-sex marriage.

Maurice Blackburn principal Liberty Sanger told the ABC the letter was “uncalled for” and “a very heavy-handed response”.

“Now it may well be that their intention was to try and frighten us into not participating in the debate,” Sanger said. “If that was the objective, well it’s ... obviously had the opposite effect.”

A spokesman from Football Federation Australia confirmed it too received one of the letters and would not be changing its stance.

Last week a booklet warning that “same-sex friendships” are very different from “real marriages” was distributed to school students around Australia as part of the Catholic church’s lobbying against changes to the Marriage Act.