BRUSSELS — Facing a decision on whether to impose tight restrictions on a booming market for electronic cigarettes, members of the European Parliament received a pleading letter in September that was signed by thousands of former smokers worried that “the positive story of e-cigarettes may be about to come to an abrupt halt.”

The signatures had been collected via a website, saveecigs.com, which proclaimed itself the voice of the “forgotten millions in this debate” — people who had taken up e-cigarettes to stop smoking, and their grateful families.

The website, however, was not quite the grass-roots effort it claimed to be. The text of the letter it asked people to sign was drafted by a London lobbyist hired by Totally Wicked, an e-cigarette company. The website had been set up by a British woman living in Iceland who had previously worked for the owners of Totally Wicked.

As the headquarters of the European Union, Brussels sets regulatory standards that resonate around the world. It rivals Washington as a focus for corporate lobbying, with an estimated 30,000 professional lobbyists with registered lobbying firms and thousands more who operate beneath the radar.