Three million people have just a 50% chance of getting their full pension benefits, a report has warned.
The credit crisis has left many final salary schemes with a black hole and not enough cash to meet future commitments.
Despite employers pouring in £120billion extra contributions over the past decade, deficits remain at over £400billion.
More than 11 million people rely on defined benefit schemes.
The Pensions and Lifetime Savings Association says most schemes will manage, but it will be “50-50” of three million pensioners getting full benefits.
Cases such as the collapse of BHS have put pensions under the spotlight.
Ashok Gupta, chairman of a PLSA taskforce, warned that without change there was a “real possibility” of more high-profile company failures.
The PLSA has called for schemes to be standardised and simplified to reduce costs to pensions firms.
A spokesman for The Pensions Regulator said: “While some schemes are facing significant challenges, over the longer term most will be able to pay their promised benefits. We are prepared to use our powers where employers and trustees fail to tackle problems.”
Pensions experts accused the PLSA of scaremongering.
Independent pensions expert John Ralfe said: “The PLSA … wants to turn the clock back to the days when companies could walk away from their pensions without fully funding them.
“There is no crisis in DB pensions, so there is no need for crisis measures.”