WA premier disappointed by document leaks

West Australian Premier Mark McGowan says he is disappointed internal documents have been leaked to the opposition following the state budget last week.

The first leak was a six-page document marked for "internal use only" about "contentious issues" regarding the state budget and directing Labor MPs on how to answer questions.

The Liberal opposition was also sent a document advising Labor MPs about the progress of issues, including a dispute with the WA Police Union and negotiations regarding Perth Stadium.

Mr McGowan described the leaks as "unpleasant" and urged whoever was doing it to stop.

"Obviously we'd like to know who's responsible for it. It's not something you prefer to happen in government," he told reporters on Wednesday.

"The main thing we're focused on is getting on with the job of getting the finances back on track, making sure that we get our budget through the parliament and get Western Australia back on a good financial footing."

Opposition Leader Mike Nahan said the leaks were coming from the same email but would not disclose his source.