The State Government is under pressure to stop ministers trading in speculative shares in WA resources companies after Labor promised a blanket ban, if elected.
Deputy Premier Kim Hames and Local Government Minister John Castrilli have directly bought and sold hundreds of thousands of shares since January last year.
But because the ministerial code of conduct allows personal share trading on the condition that members of Cabinet declare their trades, Dr Hames and Mr Castrilli cannot be in breach of the guidelines.
"We will change the code of conduct so ministers can't buy and sell shares," Opposition Leader Mark McGowan said.
"It's a no-brainer.
"I think the public would have an expectation that the highest standards would be enforced and that ministers could not benefit from privileged information that only they may receive."
Mr Castrilli told the Parliament last year about shares bought through his family trust in WA's Aragon Resources and Empire Oil and Gas.
He also invested in WA iron ore, gold and uranium explorer Enterprise Metals shares.
Soon after his purchase, shares in Empire leapt after it announced a gas discovery north of Perth.
_The West Australian _is not suggesting the minister had inside information and he correctly declared his shareholding.
Mr Castrilli said Cabinet ministers had to adhere to processes to manage perceived conflict of interests.
If something arose that had a bearing on his shares, he would be excluded from Cabinet for it.
Mr Castrilli would not reveal how many shares he bought and sold or their value.
Dr Hames, who declared his 400,000 Tectonic Resources shares on February 23 last year, said he complied with the code of conduct.
The Health and Tourism Minister said he avoided directly owning shares that could be perceived to have a conflict of interests.
Premier Colin Barnett said WA's code was enough to deal with potential or perceived conflict of interests but "it is preferable that ministers do not trade in shares".
"I sold my shares when I became a minister," he said.
Federal ministers must sell all their shares other than those in managed or superannuation funds.