The Pensions Regulator has warned employers not to cook up plans to dump their pension schemes.
Pensioners protesting outside a Labour Party conference
Companies have been warned they may be breaking the law if they transfer their schemes to new employers without meeting their financial obligations.
The regulator says it has seen a number of plans to do this without making sure the pension scheme is properly funded.
Pension scheme trustees have been told to make sure employers do not get away with it.
The regulator's chief executive Tony Hobman said: "We are starting to see proposed corporate transactions involving schemes where the primary intent behind the transaction is for the employer to abandon the scheme.
"We do not consider that abandonment of a scheme by its employers is usually likely to be in the best interests of scheme members," he added.
He told trustees that they should apply an "extremely high level of scrutiny" if any such plan came their way.
What the regulator is worried about are attempts to transfer a pension scheme to a new, nominal, employer which in reality does not have the finances to properly support the pension scheme it is taking on.
If the scheme later ran into trouble the new employer would be in no position to bail it out.
A spokesman for the regulator said that so far it had seen fewer than five examples of employers who had suggested abandoning their schemes this way.
But the fact that such a public warning is being made is a clear indication of the dangers of what might be an emerging trend.
Section 75 of the Pensions Act 1995 says that if a solvent employer wishes to stop running a scheme altogether - in effect winding it up - then it must pay the cost of transferring it, fully funded, to an insurance company to guarantee that accrued pensions can always be paid.
This would always be extremely expensive, even for a scheme with a surplus, because the insurance company would charge a large amount of money, based on the assumption that the pension scheme's assets would be invested largely in bonds, plus a margin for its own profit on top.
Kvaerner pension scheme
However, earlier this year the regulator gave its blessing to a plan apparently similar to the one which it is now warning against.
It allowed the former Kvaerner shipping and construction company - now renamed TH Global - to give up responsibility for its pension scheme in return for paying in £100m over the next six years.
The scheme, which has 32,000 members, had a deficit of around £250m.
The Regulator has refused to explain exactly why it took this decision.