"Sunrise host Nat Barr has grilled Anthony Albanese's government about why voters have been banned from using a cross to vote against the Voice to Parliament - but Yes voters can still just use a tick.

Her question comes after Electoral Commissioner Tom Rogers triggered a debate by telling Sky News 'a tick will be accepted as a formal vote of Yes, but a cross will not be accepted as a formal vote'.

The voting paper will require the word Yes or No to be written in a box. This will be made clear in instructions issued by the Australian Electoral Commission.

Barr asked Albanese government minister Jason Clare: 'Should a cross be accepted as a no vote if the electoral commission is going to accept a tick for the yes?'

Clare hit back, arguing the same strategy had been used in the 1999 republic referendum and hadn't caused any confusion.

'When John Howard held a referendum with the public, same rules, worked fine and I believe there were less than one per cent of informal votes,' he said.

'John Howard didn't want us to become a republic, he was urging people to vote No and these were the rules put in place.

'I think that pricks the bubble of the argument that this is going to cause confusion.'

Yesterday, opposition Leader Peter Dutton said voters should be able to validly use a tick or cross on their ballot paper, and that he would write to Rogers seeking clarification on his comments.

But Barr then asked Deputy Opposition Leader Sussan Ley why she hadn't raised concerns about the ballot several weeks ago when it was going through parliament.

'If a tick counts for Yes, then a cross should count for No. It's as clear as that,' he told radio station 2GB on Thursday.

'Otherwise, it gives a very, very strong advantage to the Yes case.'

'We're bringing it up now. It's actually a matter for the AEC (Australian Electoral Commission),' Ms Ley told the Sunrise host on Friday.

'We want a fair referendum, the rules have to be fair.'

However, Ms Ley argued Australia was now in the 'modern era' and that rules used almost three decades ago in 1999 were no longer applicable.

'We have a lot more Australians who can't speak English and we want everyone to vote in this referendum, so quite simply, what would people think?'

'A tick is Yes, a cross is No,' she declared.

Mr Clare said if the Opposition had been 'serious' about the ballot format they would have attempted to change the laws several weeks ago.

'The fact we are using the same rules that have been in place for 30 years and at the last referendum there was an informal vote of less than one per cent, it tells you that this is all politics,' he said.

The revelation has attracted strong criticism from the opposition, who say the Yes vote will have an unfair advantage when Australians have their say later that year.

Former Prime Minister Tony Abbott said the advice appeared to be evidence that authorities were trying to support a Yes result winning.

'The problem with all of this is that there's a suspicion officialdom is trying to make it easier for one side,' he told 2GB's Ben Fordham.

'At least as initially reported, it seems that it's going to be easier to get a Yes vote than a No vote, if a mere tick is going to count for a Yes but you've got to specifically write 'no' to vote No.

'This is the worry all along - that there is there is a lot of official bias in this whole referendum process.'

Commissioner Rogers has shrugged off accusations the move would play in the favour of the Yes vote, saying: 'No, not all. They couldn't be taken that way."