Yesterday's advice will help the European Commission produce the final draft of the new EU Pensions Directive, which is expected to be presented towards the end of the year.
The letter said the new Directive could force all remaining defined benefit pension schemes to close, while it could push many businesses into insolvency, leading to job losses.
Joanne Segars, NAPF chief executive, said: "We are disappointed Europe's pensions and insurance regulator is still proposing Solvency II-type rules for pension schemes, even though its own advice now acknowledges the damage that would be done to European pensions, jobs and the wider economy.
"Solvency II would pile extra pressure on firms that are struggling to survive during these difficult times. The NAPF's initial assessment shows that these rules could cost UK pension funds at least an extra £300bn. Faced with extra funding demands, many companies would have no choice other than to close their final salary pension schemes.
"We are pleased that EIOPA has heeded our advice on the fundamental role of the forthcoming Quantitative Impact Study in assessing the impact of its proposals on pensions and the wider economy, and that it has made its recommendations conditional on the results.
"The UK already has a strong system in place to protect its final salary pensions. It does not need additional protection from Europe. The European Commission and EIOPA should instead focus on where they can add real value. Their plans to improve defined contribution pensions and member communication are welcome, and we encourage the Commission to focus its attention on these areas."
Zoe Lynch, partner, Sacker and Partners added: ??"Like many industry commentators, Sackers are deeply concerned by the possibility of Solvency II standards being applied to UK pensions schemes. The main problem is that EIOPA has been given a narrow remit by the EU Commission - notably, the Commission has asked how funding requirements should be further harmonised, not whether they should be.?
"Given that there is no standard approach in the provision of occupational pensions across the EU, our view is that it is illogical to attempt to apply a narrower framework to all Member States, than currently exists in the IORP Directive.
"The last decade has seen significant decline in defined benefit (DB) pension provision due to increasingly stringent regulation and high costs.
"From the information provided, it appears likely the introduction of the HBS would signal the end of DB pension provision in the UK. The proposed introduction of the HBS approach represents a real risk that employers will abandon the idea of funded schemes (both DB and DC) if the solvency or minimum capital requirements are applied. The downgrading of pension benefits is a likely consequence of such increased regulation and cost - effectively the opposite result to the outcome of member protection that the Commission is seeking to achieve.?
"We appreciate that EIOPA has been asked by the Commission how funding requirements should be further harmonised, not whether they should be. However, the proposals take insufficient account of the robust regulatory environment in the UK policed by the Pensions Regulator nor the fact that occupational DB provision is a not-for profit arena and not a competitor of the insurance industry."