In May last year, while the Abbott government was grappling with what to do about gay marriage, lobby group Australian Marriage Equality was hitting the phones to corporate Australia.

Big brands like Qantas, Commonwealth Bank and Telstra signed up for a full-page newspaper ad. One of the most enthusiastic recruits was Tony Frencham, regional head of Dow Chemical.

"I was almost breaking my computer to get in there and support it," he remembers. "I didn't go and ask anyone in Dow. I didn't say: 'Am I allowed to do this?' But I knew I didn't have to."

AME now boasts more than 1000 corporate supporters, including the AFL, Network Ten and American Express. But lending your logo to a popular cause is one thing. Putting your business, your property and your brand on the line during a bitterly-fought, highly-politicised plebiscite is another.