Days before members of the European Parliament vote on a raft of new anti-smoking measures, organisers of the Save E-cigs Campaign said medical regulation of the product would condemn "Europe's seven million e-cigarette users to a premature death".
"Medicinal regulation will impose limitations on e-cigarettes ... and will limit their availability, raise costs and reduce innovation," a statement said.
"If MEPs vote for medicinal regulation more people will smoke (tobacco) and we will all be forced back to a nightmare we thought we had left behind."
Parliament next week examines new legislation to be introduced across the European Union to replace rules dating back to 2001, in hopes of reducing the 700,000 deaths attributed to tobacco across the bloc each year.
The UN's World Health Organisation (WHO) has said the safety of e-cigarettes "has not been scientifically demonstrated... (and) the potential risks they pose for the health of users remains undetermined".
But e-cig users and makers, who say turnover has doubled since 2010, claim the electronic product represent a "public health revolution that has the potential to save millions of lives".
Citing academic studies, they say e-cigarettes are safer than conventional ones and are rapidly building market share.
Electronic cigarettes look like their traditional counterparts but powered by a battery, they vaporise a solution containing nicotine or flavours which the user then inhales.
The new EU rules also include a ban on menthol and other flavoured cigarettes as part of a crackdown on youth smoking while ordering mandatory health warnings on packaging.
If approved, the new law could be in force across the 28-nation bloc within three years.