It estimates up to 29% of producers are struggling to remain profitable, even selling some produce as a loss-leader.
The findings reflected the state of the industry, not just in the UK but also the Republic of Ireland and the Netherlands, said Andrew Middlebrook, chairman of the Mushroom Bureau.
"Buyers have taken advantage of an oversupply situation in the past and are strong negotiators," he said.
"But if they want a vibrant and sustainable industry in the future they should be aware of the current situation."
Last year similar warnings were sounded by Warwick University, which identified that some 12 suppliers accounted for 90% of sales despite a predominance of smaller suppliers.
While the market continued to expand through imports and was worth £170m, English growers now only accounted for 53%. The report stressed a basic rethink was needed to protect share at a time when the rsp of £1.96/kg had not changed for six years.
It recommended a more structured method of operation that separated composting, growing and marketing - and urged suppliers to work more closely with one another. It added that the adoption of robotic picking could help to reduce labour costs.
Last June the industry launched a voluntarily supported £100,000 campaign linking some 30 growers and marketing companies from Ireland, Belgium, the Netherlands, Poland and Ireland with their counterparts in the UK.
Middlebrook said the response had been so favourable that there would be a further campaign this year at the same level targeting consumers during the spring and summer - historically a period of lower sales.
Among the plans will be a free booklet and an upgraded web site.