The Diet on Wednesday passed an amendment that will ban smoking in public facilities for the first time as the nation — long deemed a haven for smokers — scrambles to combat secondhand smoke in the lead-up to the 2020 Tokyo Games.

The ban will be implemented in stages, coming into full force by April 2020.

The revision to the Health Promotion Law, however, has been significantly watered down from the health ministry’s original proposal, falling short of a comprehensive smoking ban in restaurants and bars.

Under the updated law, an estimated 55 percent of eateries nationwide will end up being exempt, prompting criticism that the amendment, although a step forward, is a far cry from the anti-smoking ordinance adopted by the Tokyo Metropolitan Government just last month, a move expected to make more than 80 percent of eateries across the capital effectively smoke-free.

Having long urged operators of public facilities to merely “make efforts” to curb passive smoking, the revised law will make smoking in some designated institutions illegal for the first time, penalizing noncompliant operators and smokers with fines of up to ¥500,000 and ¥300,000, respectively.

The measure, according to the health ministry, is expected to raise the World Health Organization’s grading of Japan’s anti-smoking efforts by one rank — to the second-lowest level.

The amendment was watered down after facing fierce resistance from the ruling Liberal Democratic Party and industry groups. Japan has long been soft on smoking due largely to vested interests and pork-barrel politics, a system in which the tobacco industry has thrived. Even corporate giant Japan Tobacco Inc. is partially owned by the Finance Ministry.

Specifically, the amendment declares the premises of public institutions such as schools, hospitals and municipal offices as nonsmoking. This means smoking will be prohibited both indoors and outdoors in principle — although smoking spaces can be set up outside those buildings.

A less rigorous measure will apply to other public facilities, including restaurants and bars, where only indoor smoking will be outlawed. But even inside, smoking will be allowed in segregated, well-ventilated rooms, where no drinking or eating will be permitted.

Smaller restaurants will be exempt altogether. Some proprietors of izakaya (Japanese-style pubs), for example, have voiced fears that an outright ban could hollow out their customer base, which they claim is underpinned by smokers. But multiple studies conducted overseas have shown that nonsmoking policies have little to no adverse effects on businesses.

Still, under the amendment, establishments capitalized at ¥50 million or lower and with a floor space of up to 100 square meters can choose to allow smoking if they put up a sign warning incoming customers.

People under the age of 20, however, will be prohibited from entering these establishments. Newly established bars and restaurants will be obliged to ban smoking, regardless of size.

The revision is a “welcome” development in that it penalizes violators, but still falls “significantly short” of global standards in terms of effectiveness, said Mikio Kawamata, a professor of rehabilitation studies at the Kyushu University of Nursing and Social Welfare.

“It’s a real pity that the revision didn’t even match up to the standards upheld by Tokyo,” Kawamata said.

Rather than zeroing in on the size of each restaurant, the Tokyo law imposes a smoking ban on any establishment with at least one employee on the payroll, underscoring a goal of protecting those deemed particularly vulnerable, such as workers and children.

Kawamata also took issue with the fact that the national amendment allows smoking spaces to be established on the premises of schools and hospitals.

He likewise criticized the leniency with which users of increasingly popular heat-not-burn cigarettes will be permitted to dine and drink in ventilated smoking rooms under the revision — which means employees who serve them will remain susceptible to secondhand smoke.

While it is true that there is no sufficient scientific evidence proving the adverse health effects of passive smoking caused by e-cigarettes, “more and more recent studies have provided data verifying their harm,” Kawamata said, adding that stricter regulations against e-cigarettes may be needed in the future.