Former Health Services Union boss Kathy Jackson has pleaded not guilty to 166 theft and deception offences, as she was committed to stand trial over the misappropriation of half-a-million dollars of members' money.

Ms Jackson entered the plea on the first day of her committal hearing, cutting short what was expected to be a four-week hearing in the Melbourne Magistrates' Court and forgoing the opportunity to cross-examine witnesses.

The one-time union whistleblower has consistently denied misappropriating Health Services Union funds between 2003 and 2011.

She has been accused of stealing more than $490,000 of union funds.

Police allege Ms Jackson used thousands of dollars to pay for flights to Hong Kong, New Zealand, Bali and the United States.

She is also accused of using union credit cards to pay for overseas accommodation, including stays at the Bellagio Hotel and Casino in Las Vegas.

Ms Jackson allegedly used union money to buy herself more than $1,000 in goods from electronics store JB Hi-Fi and a Mercedes Benz for her ex-husband, Jeff Jackson, who is a witness in the case.

Jackson allegedly claimed treadmill as union expense

It is alleged Ms Jackson also spent $1,065 of union funds to hire a treadmill in November 2007, which she claimed as a general union expense, and $4,636 on artwork in March 2009, which she later claimed as a conference expense.

She is also accused of claiming she was entitled to an annual $21,000 "honorarium" in addition to her wages in June 2010, and that she needed to be back-paid for the previous three years.

That allegedly resulted in a $63,000 payment which she was not entitled to.

Ms Jackson is facing a total of 147 charges of obtaining financial advantage by deception, 18 counts of theft and one charge of obtaining property by deception.

Ms Jackson appeared in court with the support of her partner, the former vice-president of the Fair Work Commission Michael Lawler.

More than 60 witnesses were expected to give evidence during the month-long hearing.

Ms Jackson, who remains on bail, will appear in the County Court for a directions hearing on Tuesday morning.