There are suspicions someone with insider information of the federal election date may have tried to profit by placing bets on the date before it was announced.
Sportsbet says it shut down the market for the federal election date when it received a suspiciously high number of bets for a September poll on the morning Prime Minister Julia Gillard announced it.
Sportsbet's Haydn Lane says the bets were not huge, but there were enough of them to raise suspicions.
"There was a couple of different punters having bets in the hundreds of dollars," he said.
"With the odds being 167 into $1.50, you know, they're standing to make either 67 per cent or 50 per cent return on their investment, so it wasn't as though they were getting set to win thousands but certainly hundreds if accurate.
"But the reason we suspended betting, it was more to get an understanding of what's happening, if there was any news or if there was potentially a leak, because with that particular market, there hadn't been really much activity at all over the previous couple of weeks and then we start taking bet after bet."
Mr Lane says there were only 10 bets placed but they raised suspicion because they were placed in such short succession.
"We obviously weren't aware of any inside information, but the fact that we took bet after bet and again, there weren't tens or hundreds of these bets, but they were in a succession," he said.
"So the prudent thing for us to do was to suspend the market until we could get a better gauge of what was going on, hear of anything.
"As it turned out, there was an announcement shortly afterwards."
Aside from a handful of political allies, Ms Gillard took most people by surprise last Wednesday when she announced the date of the election, which raises the question - who had the inside running?
But Mr Lane says it is of no great concern for Sportsbet.
"In this case we weren't actually sure, but we thought the prudent thing to do was to suspend it and as it was, it was proven correct," he said.
Independent Senator Nick Xenophon has drafted legislation which would ban betting on politics. He says it is open to corruption.
But Mr Lane says Sportsbet has safeguards in place to protect the integrity of political gambling.
"You could argue that some people had some inside information here and took advantage of that. What we do in that case is put low limits in place," he said.
Independent MP Andrew Wilkie says the matter must be investigated and has again called for betting on elections to be banned.
"If it was a member of staff of a politician it would appear to be at odds with their employment contract," he said.
"They should at least be disciplined, but more broadly the Government needs to take action to stop this, to outlaw it."
Regardless, Sportsbet has paid out on all bets for the election being held in September.