Bickering over campaign financing has already begun barely a day after the federal government set the ball rolling on the same-sex marriage plebiscite.

The Yes and No camps are accusing each other of deception and trickery over the sources of funding for what is expected to be a combined campaign spend upwards of $60 million.

“This is a David and Goliath battle,” Australian Christian Lobby managing director Lyle Shelton told ABC Radio’s AM program.

“We don’t have George Soros’s overseas money like we saw in Ireland with the pro-same-sex marriage campaign,” he said in reference to the well-known progressive American billionaire.

“We’ll be appealing to mums and dads, we’ll be appealing to donors everywhere, we need to raise a lot of money to fight a national campaign.”

Tiernan Brady headed the successful Irish campaign to introduce same-sex marriage, and now heads the Yes campaign in Australia.

He told AM Mr Shelton’s claims of being the underdog were a distraction.

“I think most people would laugh at that when they heard it out loud,” he said.

He said the postal plebiscite had been designed to help the No campaign.

“This entire process is designed to put the people who believe in marriage equality at a disadvantage.”

He declined to talk directly about the sources and quantum of funding for the Yes camp’s campaign when asked.

“No amount of money anywhere will ever replace the power of a conversation,” he said.

‘Brace yourself’

Mr Shelton did not rule out accepting overseas money for the No campaign.

“If there was some way to prevent money coming in from overseas for the other side, we would welcome that,” he said.

“But we’re going to have to try and raise money wherever we can and that will principally be from Australia.”

Veteran Labor-aligned political strategist Bruce Hawker is predicting an expensive and hard-fought battle ahead for both sides.

“We’re going to be seeing this full on for the next few months, just brace yourself for it,” he told AM.

He said the combined campaign spend could easily top $60 million.

“For something like this, conservatively, you’d need something like $20 million or $30 million to make any impression at all.”

– ABC