The alternative flag designs fly outside The George Hotel in Park Avenue, Christchurch. The Electoral Commission is warning New Zealanders against posting photos of their completed flag voting papers online.

Kiwis posting photos of their completed flag voting papers online are breaching the spirit - if not the letter - of the law, the Electoral Commission has warned.

A number of New Zealanders - including one MP - have been sharing photos of their completed ballots on Twitter.

Many of those posting photos are spoiling their votes as a protest against the decision to hold a referendum.

According to the Electoral Commission's rules for the flag referendum, it is an offence to "print, distribute or deliver an imitation voting paper together with any direction or indication as to the option for which any person should, or should not vote, or content likely to influence any vote".

Posting an image of a completed referendum voting paper online "appears to be contrary to the spirit and purpose" of the secrecy of the voting process and the rules on imitation ballot papers, according to the commission.

Green MP Gareth Hughes, a staunch Red Peak advocate, was among those to post photos of their completed voting papers on Twitter.

Hughes said he took the photo down after being alerted that it may fall foul of the law.

"It looks to be a bit of a legal grey area so i thought to avoid any uncertainty, it was best just to remove the image."

However, electoral law expert Graeme Edgeler said sharing a photo of a completed voting paper was unlikely to be illegal, as the commission's rules were intended to prevent people from mistakenly using a false ballot.

"The Electoral Commission might think it's against the spirit of the law...but the spirit of the law doesn't create a criminal offence.

"They might frown on people doing this, but I can't see a problem: it's part of the democratic process really, you vote how you want and if you want to shout from the rooftops, you can."

An Electoral Commission spokeswoman said any complaints about photos of completed voting papers would be assessed on a case by case basis.

The spokeswoman also downplayed fears that the unique identifier QR barcodes on the ballots, and pictured in some of the online photos, could lead to electoral fraud.

Any instances of two voting papers being submitted with the same QR code would be "escalated" by the commission for investigation, she said.

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