European lawmakers on Tuesday were set to tighten rules governing the multibillion-dollar tobacco market by imposing bigger and bolder warnings on cigarette packs, banning most flavorings like menthol and strengthening regulation of electronic cigarettes.

The European Parliament vote in Strasbourg comes after months of bitter debate. Tobacco lobbyists decry the regulation as disproportionate and limiting consumer freedom, while European officials advocate the benefits to public health.

Under the proposed law, mandatory warnings would take up to 75 percent of tobacco packaging and be more prominent, with the inclusion of gruesome pictorials—some for example showing cancer-infested lungs—to discourage potential customers. It also aims to stop youngsters being swayed into smoking by new, fancy packaging, e-cigarettes or cigarettes featuring flavors such as menthol or fruit aromas.

Smoking bans in public, limits on tobacco firms' advertising and other measures over the past decade have seen the number of smokers fall from an estimated 40 percent of the EU's 500 million citizens to 28 percent now. Still, treatment of smoke-related diseases costs about 25 billion euros ($34 billion) a year, and the EU estimates there are around 700,000 smoking-related deaths across the 28-nation bloc.

The issue proved highly divisive in Parliament, and last-minute amendments sought to water down the legislation, for instance seeking smaller mandatory warning on cigarette packages.

Ireland's Prime Minister Enda Kenny on Monday wrote a fervent appeal to lawmakers, urging them to stick to the bigger warning labels since "they are more effective at highlighting the dangers of smoking."

"Every year, more Europeans die from smoking than from the combined total of car accidents, fires, heroin, cocaine, murder and suicide," he said.

If a majority of lawmakers backs the legislation, Parliament must still reach a compromise with the EU governments on certain points before the rules can enter into force. Diplomats say a deal could be struck by the end of the year.

However, if lawmakers decide they want more time to evaluate the measures, adoption of new rules would run into procedural hurdles and collide with elections for a new European Parliament in May, likely delaying the legislation until early 2015.

The draft law would also limit the booming sector of e-cigarettes by demanding they be sold as therapeutic devices to help smokers kick the habit, rather than as a casual alternative to tobacco. The battery-operated products look like real cigarettes and turn nicotine into a vapor inhaled by the user. They are often marketed as a less harmful alternative to tobacco.

The tobacco industry has fiercely lobbied against the new rules, in an effort that officials and diplomats described as an unprecedented campaign to intimidate lawmakers and soften or frustrate the legislation.

The head of the World Health Organization, Margaret Chan, on Monday urged Parliament "to remain steadfast in the midst of these pressures" and to stick to the proposals "to abate the entirely avoidable deaths and diseases brought on by tobacco use."

"The tobacco industry is, once again, using an arsenal of economic arguments, precisely because such arguments are so effective in shifting the emphasis away from health, especially in times of financial austerity," she said.

The lobbying was led by Philip Morris International Inc., which owns several brands like Marlboro and called the new legislation "deeply flawed." The company maintains that, among other things, banning menthol, slim cigarettes or small packages would violate EU rules.

Philip Morris, with $8.5 billion of sales and 12,500 employees in Europe, also claimed the regulation could result in up to 175,000 job losses and lost tax revenues of 5 billion euros per year.