It was revealed on Thursday that Palas owns shares in Transurban, which will earn about $ 37 billion in road tolls in Melbourne from a contract for the construction of the Western Gate tunnel, according to research by the Parliamentary Library.
Transburne is one of the favorites on the Australian Stock Exchange in recent months, with road operator shares climbing more than 19 percent since October.
Mr Palas says he respects all the rules that require him to disclose his financial interests.
"I was completely transparent in this regard, I respected all obligations," he said in the middle of the morning.
"In essence, it's a setup and forgetting foundation. In 2011, when the Fund was established, Transurban was not in that group of investments … some time later it came in
"I have never paid attention to, until yesterday, what was in that fund."
But Mr. O'Brien said the treasurer's stock in Transurban was a clear conflict of interest and he should be fired.
"The treasurer personally benefits from his Transurban investment at the expense of Victorian drivers who will pay billions of dollars to higher tolls," he said.
Mr O'Brien said Prime Minister Daniel Andrews must at least conduct an independent investigation and the treasurer should withdraw while it is being implemented.
Mr O'Brien described these findings as a scandal.
"This is a conflict of interest 101," said the liberal leader. "You can not own shares in a company while you work with that company. This is embarrassing, this is unethical".
Mr. O'Brien said that he does not own shares during his time as a treasurer and does not own it today.
"The work of the treasurer is to put money in Victoria's pockets, not to lay their pockets," he said.
Noel Tove is a state political editor for age
Benjamin is a state political reporter