"Harmful market practices" have been highlighted in an ACCC report into the nation's wine industry.
The Australian Competition and Consumer Commission released its interim wine grape market study on Monday.
Among the major issues identified was a lack of transparency on price and how grapes were assessed for quality.
Transportation costs, bio-security rules and a high-degree of market concentration are also issues which reduce competition.
The market study included feedback from warm climate wine grape growers in Griffith and the Riverina, the Riverland in South Australia and Victoria's Murray Valley.
Increased transparency over indicative and final prices is likely to lead to greater competition between winemakers.ACCC deputy chairman Mick Keogh
"We found that winemakers do not publicise the prices they pay to growers and often have confidentiality terms to prevent growers from disclosing their indicative and final prices to other growers," ACCC deputy chairman Mick Keogh said.
"Meanwhile, various supply arrangements appear to favour incumbent buyers of bulk wine grapes, such as exclusive supply clauses, automatic and long term contract extensions, and difficult contract termination obligations on growers."
The interim recommendations require warm climate winemakers publicly release indicative and final grape prices to a third party.
Standardised testing for wine grape quality assessments needs to be developed, and growers need to be paid within 30 days of grapes being delivered.
The recommendations also suggest the dispute resolution processes in the Australian Wine Industry code of conduct are improved.
"Increased transparency over indicative and final prices is likely to lead to greater competition between winemakers, and better outcomes for growers," Mr Keogh said.
Riverina Winegrape Growers chairman Bruno Brombal said at first glance, the report's findings were "promising" for grape growers.
Mr Brombal said there were around 10 or 12 growers who spoke to the ACCC during their visit to the area in November last year.
He said the report was extensive and emphasised the need for more time to examine the details.
"There's a few things that we need to look at and we'll be putting a submission in," Mr Brombal said.
The ACCC's final report is expected in September, and submissions on the interim report are open until June 28.
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