At worst, the letter states, it would push many businesses into insolvency, leading to job losses.
The joint letter has been sent as early this week the European Insurance and Occupational Pensions Authority (EIOPA) will send its final advice on the EU Pensions Directive to the EU Commission, and there is a strong risk it will recommend Solvency II as a framework for the directive.
Joanne Segars (pictured), chief executive of the NAPF, said: "These plans would cause massive damage to UK pensions and undermine economic growth across Europe. Instead of making pensions more secure, they would have the opposite effect.
"Solvency II type rules would put extra pressure on companies struggling for survival, and also force them to divert money away from investment and new jobs. Faced with extra funding demands, many businesses will simply shut their final salary pension down.
"The European Commission will receive a crucial submission this week from its own advisers on how to take the project forward. We believe a comprehensive impact assessment is needed before any decision to go ahead.
"The UK already has a strong system to protect pensions. During these tough economic times, Europe should focus on fostering growth and job creation instead."