The incident is seen as a threat to Ms Jackson for her role in the Craig Thomson scandal engulfing the labor party. Victoria Police this morning told this website they were investigating after the shovel was found outside the front door of Ms Jackson's home in an eastern Melbourne suburb this morning.

The Age understands the shovel has been seized by police, who are examining it for forensical clues.

Ms Jackson is giving a statement at a Melbourne police station this morning.

Asked about the incident, Ms Jackson told The Age: "I don't want to comment about it at this point in time".

Neighbours of Ms Jackson told police they saw a car acting suspiciously outside the home about 2am today, The Age understands.

It comes as the Labor Party was engulfed in mounting internal turmoil last night after long-standing tensions boiled over in response to the Thomson affair.

Mr Thomson, the Labor member for the NSW seat of Dobell, is accused of having misused his union credit card while he was an official of the HSU, with spending on escort services and unexplained cash withdrawals worth more than $100,000.

Party figures are furious that Ms Jackson had chosen to refer the Thomson affair to the police.

As Prime Minister Julia Gillard went on the attack against the opposition over its pursuit of the affair yesterday, she faced unwelcome pressure on a new front as senior Labor figures in Victoria threatened recriminations against the trade union at the centre of the affair.

Sources told The Age that they were looking at ways to punish the Health Services Union after the decision by Ms Jackson to provide assistance to a NSW police inquiry into allegations against Mr Thomson.

Senior Labor figures in Victoria were last night considering a possible ban on the HSU from taking part in the party's key policy and administrative forum, the state conference.

They were looking at using the union's alleged failure to file audited reports to Fairwork Australia as a pretext for its exclusion from the conference.

If Mr Thomson quit Parliament before the next election, this would force a byelection that could leave Ms Gillard without the numbers to govern.

While Mr Thomson's seat is in NSW, the party's response to the controversy surrounding him has been particularly bitter in Victoria, where the party's Right faction has split and the HSU has been the focus of a battle between Right warlords.