The World Health Organization (WHO) on Tuesday called on Beijing legislators to fix the loopholes in the city's upcoming indoor smoking ban legislation.

The Beijing Municipal People's Congress will on Thursday go through the second reading of a draft law that would ban smoking in all indoor public places, a step toward meeting its commitment to cut down on indoor tobacco use in a convention ratified with the WHO in 2005.

The WHO, however, expressed worries that a major loophole in the draft law which would allow smoking in "single occupancy" work places might weaken the law and create imbalance in its enforcement.

As the draft is currently written, smoking would still be permitted in offices occupied by a single person, usually leaders and senior staff.

"Exceptions to the new law that provide special privileges for senior managers and officials would foster a perception that China has one rule for its elites, and another for its workers," Bernhard Schwartlander, WHO representative in China, wrote in a letter sent to the media as part of their government lobbying campaign.

Schwartlander urged Beijing to "set a precedent" in its anti-smoking ban, saying that only a comprehensive ban will comply with the terms of WHO's Framework Convention on Tobacco Control, which China signed in 2005.

The convention obligates China to adopt laws that protect citizens from exposure to tobacco smoke in offices and other indoor public places.

"We have reached out to the Beijing People's Congress on this matter … and we are optimistic that the Beijing lawmakers would listen to our concerns," WHO Tobacco Free Initiative in China's Angela Pratt told the Global Times on Tuesday.

The draft would also allow hotels and airport waiting halls to build "smoking rooms with independent ventilation systems," although some expressed skepticism at the effectiveness of these rooms at preventing second-hand smoke.