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."
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".
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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.
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.