Swansea City's Supporters Trust fears the club's future could be "at risk" if the right action is not taken to deal with the financial impact of the coronavirus crisis.
It has also called on the Professional Footballers' Association to change its stance and accept players' wage cuts to stop teams falling into administration.
The Trust says it is a "harsh reality" that costs cannot remain the same.
A statement called for "appropriate action" to counter the threat.
It comes after English Football League chairman Rick Parry said that clubs face a "£200m hole" by September, adding that there were sides "racking up creditors" and it was "difficult to say" how many clubs could go out of business as a result of the pandemic.
Swansea City chairman Trevor Birch has already admitted the club - and football in general - would face "testing times".
That warning came after announcing wage deferrals for the playing squad, repayable when crowds are allowed back, which he said would only assist short-term cash-flow.
With the prospect of the season resuming behind closed doors meaning no guaranteed match-day revenue in the near future, the Trust, which owns 21% of club shares, says the situation is unsustainable.
Despite a "productive" meeting with the club, the supporters' body warns: "The future of our football club is of great importance to us all. Without appropriate action being taken, its future is at risk.
"In terms of the playing squad and management teams, we need to ensure our costs match the new realities. It is patently clear that deferring costs until some unspecified point in the future is unsustainable.
"Without promotion to the Premier League, or a significant amount of investment, there will be no realistic way to pay them in the future.
"Cuts to the wage bill and other operating costs will be necessary for the duration of this crisis, and potentially longer as the economy tries to recover.
The Trust claims the advice of the PFA to its members has to change for EFL clubs to survive.
"The longer footballers and their union refuse to accept that a cut in wages is necessary, the more chance that we will see clubs enter administration or liquidation," it said.
"This may seem unfair. However, it is a harsh reality that costs cannot remain the same when revenues are cut so dramatically."
The Trust is urging all parties to work together "to ensure the club's survival".