Last year, Mrs Rinehart subpoenaed Steve Pennells from The West Australian to reveal sources used in articles about her family. This year, she placed a similar order on Fairfax Media's Adele Ferguson.

Lawyers for Mrs Rinehart, a major shareholder in Fairfax Media, argued the information was needed for a private arbitration hearing she was involved with in NSW. The nature of that hearing is confidential.

The journalists declined Mrs Rinehart's request, citing their professional ethics to keep sources confidential.

The case against Pennells dragged on through out-of-court negotiations and occasionally heated hearings, before its dismissal on Tuesday in what is being hailed a legal victory for press freedom.

''We weren't expecting it to go our way and not so spectacularly,'' Pennells said. ''[What the judge] says about press freedom and confidentiality of sources is far above what we could have even hoped for.''

Justice Janine Pritchard's judgment reinforced WA's ''shield'' laws, which were passed with the aim of protecting journalists from being forced to disclose their sources.

The secretary of the Media Entertainment and Arts Alliance, Chris Warren, said the decision highlighted the need for national legal protection of journalists' sources. ''It is outrageous that, even with [state] shield laws in place, Steve Pennells was forced through a very lengthy, expensive and stressful series of court procedures before this decision reiterated the position of the law,'' he said.

Lawyers for Mrs Rinehart also failed in a bid to keep the judgment from being made public on legal grounds.