The sale of The Sunday Times to its rival Seven West Media would create an unprecedented level of business and media power in Western Australia unseen anywhere else in the country.
In a submission to the Australian Competition and Consumer Commission, the Media Entertainment & Arts Alliance, which represents WA journalists, urged the watchdog to impose conditions on the sale that would allow the Sunday paper to maintain editorial independence from SWM.
MEAA regional WA director Tiffany Venning said merging journalists from The Sunday Times and PerthNow website into the rival newsroom of The West Australian would create a litany of problems if they could not work independently of each other.
"There would be a threat to the diversity of news and opinion in WA if Seven West Media gained control of The Sunday Times," she told the the ACCC.
"The two papers under different owners have ploughed their own furrow. The different approaches allow the news agenda of WA to have a variety of major influences and influencers."
A transaction without editorial conditions could give SWM chairman and prominent businessman Kerry Stokes unprecedented influence over government and business interests in WA, the union suggested.
"It will put incredible power in the hands of one mogul, Kerry Stokes, whose business interests in WA extend far beyond the media to include property investment, land development, oil and gas exploration and iron ore," Ms Venning wrote.
"This involves commercial relationships with major mining groups and fellow entrepreneurs."
The WA branch also expressed doubts about SWM to objectively report on interests that affect Mr Stokes and shareholders and executives on the SWM board.
"SWM shareholders and senior executives are also heavily involved in the Perth business scene at large and in dealings with the state government," she wrote.
"These dealings ... also include attempts to acquire significant assets or significant contractual benefits through those dealings with the state government.
"There is an obviously greater potential for problems in objectively reporting or analysing these business activities, especially involving government, when that same group controls all the daily newspapers in town."
The alliance suggested a joint venture vehicle controlling The Sunday Times and PerthNow would help journalists from both newspapers maintain their independence and rivalry.
"Such a venture might go a long way to alleviate the competition concerns we, and no doubt others, have aired in submissions to the ACCC," she wrote.
Ms Venning said diversity in the opinion of news and issues that affect West Australians was paramount and must be maintained, highlighting the different stances The Sunday Times and The West Australian had on the recent shark mitigation debate.
"The West Australian editorialised in favour of shark culls... The Sunday Times took a more, well, pro-shark attitude," MEAA WA media section president Martin Turner said.
"It was a very grassroots issue in WA, and quite a strongly divisive one... but you had some nuance in the discussion because we had different news organisations giving different things prominence."
Content sharing arrangements would stifle the PerthNow website too, with News Corp content it relies heavily from, such as news.com.au, unavailable if SWM owned it.
Launched in 1897, The Sunday Times was Rupert Murdoch's first newspaper acquisition in 1955 when he was just 23, paving the way for him to create the world's biggest media empire.
Submissions on the proposed acquisition by Seven West Media should go to mergers@accc.gov.au, with the ACCC to release its findings on July 28.
