Conflict of interest claims around one state Transport Minister could become politically sticky, an analyst says.

The Western Australian Premier may have no choice but to sack Transport and Finance Minister Dean Nalder if his financial records do not check out, says political analyst Peter Kennedy.

The expert has weighed into the debate after WA Premier Colin Barnett ordered a review into Mr Nalder's financial records, to ensure that he has complied with the state's ministerial code of conduct.

The review follows revelations that Mr Nalder holds the position of director in a private company that partly owns Fleet Network.

Fleet Network leases cars to public servants under policies from the Minister's own department.

For some, making private money through a ministerial position is the definition of conflicting interests, but the WA Government wants to check further.

Speaking to the ABC this week, political analyst Peter Kennedy said if Nalder’s role in the company does breach conflict rules, the Premier may have to sack him.

“It’s up to Mr Barnett to decide just how serious it is,” Mr Kennedy said.

“If he thinks it's a minor indiscretion, then he probably wouldn't ask for Mr Nalder's resignation.

“But however if he does see it as a serious blemish it might be possible that he's got no alternative.”

The ministerial code of conduct specifically states that ministers must resign from all directorships in public and private companies.

But Mr Nalder says he has sought advice from the Department of Premier and Cabinet, the cabinet secretary and the clerk of Parliament, and has been informed of the correct way to disclose them.

Ditching Mr Nalder just a few months after he was given the job could hurt the already damaged WA Government's succession plans, which were hit this year by the departure of former treasurer Troy Buswell and former attorney-general Christian Porter.

“Mr Nalder I think had been looked upon as one of the more promising junior ministers ... Mr Nalder's another potential replacement for Mr Barnett as leader,” Mr Kennedy said.

“On the surface it does appear there has been a genuine conflict of interest. He's acted to solve it, but if he's acted in time or not we'll find in the next day or two.”

Despite previously stating that everyone knew about Mr Nalder's business background when he took office in March, WA Premier Colin Barnett now says he was unaware of his minister’s involvement until late last week.

“This arose through some media enquires late last week,” Mr Barnett said on Monday.

“So I'm doing what a Premier should do... I'm simply going to go through and have that reviewed thoroughly to make sure every financial interest is declared.

“When he became a minister, everyone was conscious he had a strong business background, so great care was taken in the preparation by himself, with the support of staff, to make sure that his declaration was accurate.

“Look there is no investigation. All that is happening is that there is a review being conducted of Dean Nalder's declaration of financial interests.

“And if there is, and it's a big 'is', any conflict of interest, then that will be dealt with.”

The Opposition has called for Mr Nalder to stand aside.