LONDON (Reuters) -British American Tobacco for years fought the sale of unauthorised, disposable vapes in the U.S. - the world's largest market for smoking alternatives - lobbying lawmakers and arguing aggressively in court that they were illegal.

But with rivals eschewing government licences and the market now worth billions, it's preparing a U-turn.

"Not having access to this world weighs on our company's bottom line," Luis Pinto, spokesman for BAT's U.S. unit Reynolds American, told Reuters as it prepared to test launch its first new disposable product in the United States since an influx of unregulated rivals hammered its sales.

Reynolds' disposable vape brand Vuse One uses laboratory-produced synthetic nicotine and has an application pending with the U.S. Food and Drug Administration. Pilot sales will start in late September or early October, Pinto told Reuters exclusively.

Campaigners, however, accuse the company of putting profits above public health. And the FDA, which regulates nicotine products, told Reuters that going to market without an FDA licence, as BAT intends to do, would break the law.

"All new tobacco products ... that are on the U.S. market without the statutorily required premarket authorisation from the FDA are marketed unlawfully," it said.

The agency did not comment specifically on BAT's strategy when asked by Reuters, but it said a pending application did not create a "legal safe harbour to sell a product."

Pinto said BAT was not adding to the illegal market and its approach would differ to unauthorised rivals: its products have been subject to due diligence, will be sold via large national retailers and their features and marketing will follow stricter policies.

"It's not about, if you can't beat them, join them," he said.

Public health authorities and researchers are divided over how to weigh the potential benefits of vaping - mainly helping smokers switch away from cancer-causing cigarettes - against risks, including underage use.

Booming sales of unregulated disposable vapes, often produced by Chinese companies, have exacerbated divisions. Some offer exceedingly high nicotine hits or flavours like "rainbow bubblegum" and "cookie butter" that critics say are targeted at youth.

The FDA is meant to assess vape products before they go to market and issue licences to those it finds to be, on the whole, beneficial to public health: reducing the burden of smoking without causing new problems, like a surge in youth sales.

But it has struggled to keep up with a massive influx of applications, leading to long delays in authorising products for sale.

In the meantime, big tobacco companies - many of whom are awaiting FDA licences - have watched from the sidelines as the market has exploded.

BAT estimates U.S. single-use vape sales hit 6 billion pounds ($8 billion), around 70% of total vape industry sales, last year.

"We should not be disadvantaged while illicit actors ... take over the market," said a spokesperson for Marlboro-maker Altria, which has also shifted its stance on synthetic nicotine products that lack an FDA licence.

U-TURN

BAT's new devices will initially go on sale in Tennessee, Florida and Georgia, and while they do not yet have an FDA licence, Pinto said they can be launched.

BAT acquired the device in April, but its previous owner applied for an FDA licence in 2022. That application has been pending long beyond the agency's 180-day mandate for reaching a decision.

Reynolds launched a nicotine pouch brand last year on the same basis. Pinto said it has never been challenged by the agency over this move.

Altria, which also previously considered synthetic nicotine products without FDA signoff as illegal, has shifted to a similar position, CEO William Gifford told investors in April.

"We're looking at all available opportunities to assess what's the right move in that direction," he said.

The company's spokesperson said it regularly assesses the market for opportunities.

It's a stark reversal for two of the industry's biggest players.

Under FDA rules, since July 2022 synthetic nicotine products have required the agency's authorisation.

Many companies, however, have simply ignored FDA rules, and the regulator has struggled to stem sales of unauthorised devices.

BAT's U.S. vape volumes have fallen by 33 million units - around 10% - since 2022. Altria in January placed its 2028 growth targets under review, citing unauthorised sales by smaller players.

Big tobacco companies initially fought back, launching lobbying and marketing campaigns, lawsuits and intelligence operations.

In 2023, Reynolds wrote to the FDA complaining that unauthorised synthetic nicotine products were on the market illegally and damaging legitimate businesses.

It also complained broadly about unauthorised disposable vape sales using any form of nicotine by smaller U.S. and Chinese players.

Pinto said, according to Reynolds' interpretation of the FDA's public response to that letter, the agency was using "enforcement discretion" for products with pending applications, meaning they could be marketed legally.

WALKING THE LINE

Others disagree.

Brian King, executive vice president for U.S. tobacco control programmes at the Campaign for Tobacco-Free Kids, said BAT's strategy was illegal and dangerous.

"Flooding the market with unauthorised tobacco products - including those with synthetic nicotine - presents a risk to public health," said King, who until April was head of the FDA's Center for Tobacco Products.

Jim McCarthy, spokesperson for trade body American Vapor Manufacturers, which has defended businesses selling unauthorised vapes amid Big Tobacco criticisms, meanwhile criticised BAT's "breathtaking audacity" in introducing Vuse One after advocating for action against competitors.

Anthony Sedgwick, co-founder of BAT investor Abax Investments, backed the company's move, which he said could boost revenues just as a Trump administration crackdown hits unauthorised imports.

"BAT will walk absolutely on the line of where the regulatory limit is," he said.

($1 = 0.7380 pounds)