Money paid as a deposit for public transport cards should be audited and details of any funds - which could contain billions of yuan - should be disclosed to the public, according to three lawyers who have called on the central government to tighten regulations on the deposit fund.

The lawyers, from Henan and Jiangsu provinces and Beijing, submitted a letter to the Legislative Affairs Office of the State Council on Tuesday urging the government to better regulate the deposit money for the country's more than 180 million public transport cards.

Wen Lihua, one of the three lawyers, said that each public transport card requires a deposit of 10 to 30 yuan ($1.57 to $4.72), and the total value of the 180 million cards, as revealed by public information, is 1.8 to 5.4 billion yuan.

"The regulation of public transport cards is messy. In some cities like Beijing, the deposit money is 20 yuan for each card, while the price in Nanjing in Jiangsu province is 30 yuan for name verified cards and 20 yuan for non-verified cards," Wen told China Daily on Wednesday.

The public transport cards' deposit fund would earn a huge amount of bank interest, and the details of this fund should be publicized, the lawyers said in the letter.

The lawyers also suggested the cost of each card be made public because the deposit required to have a card varies in different cities.

A regulation issued in 2001 by four ministry-level agencies, including the Ministry of Finance and the People's Bank of China, states that the management of public transport cards' deposit funds should be dealt with by provincial-level governments.

But not a single provincial government has required local public transport companies to disclose the whereabouts of the money they have taken as a deposit for public transport cards, according to the lawyers' letter.

Several months ago, Wen, along with Wang Yu from Beijing and Ji Laisong from Henan province, called on local governments to reveal the details of public transport cards' deposit funds, but their request was denied by the governments who told them "no such information exists".

In the recent letter the three lawyers proposed that the State Council urge provincial governments to issue regulations on transparency regarding public transport cards.

"In Nanjing, if a non-verified bus card holder loses the card, he or she could neither claim back the pre-paid money in the card's account nor get back the deposit money," Wen said. "All of the pre-paid money would be retained by the public transport company if the non-verified card was lost."

It is not the first time the public has raised doubts over transparency in the administration of public transport cards.

In March, Liu Wei, a Beijing resident, submitted a request to the Beijing Municipal Administration and Communications Card Company, the public transport card manufacturer in the capital, that it disclose information about the deposit money for the city's 40 million public transport cards.

"There is as much as 800 million yuan of deposit money for public transport cards in Beijing, and its annual bank interest could reach 28 million yuan," he said.

Liu said he has not yet received any reply from the company.

Shi Xiangyang, a member of the Beijing Municipal Committee of the Chinese People's Political Consultative Conference, first proposed the details of the public transport cards' deposit fund be made transparent six years ago, according to a report by China Youth Daily.

The Beijing Municipal Bureau of Finance replied to Shi in 2009, telling him that the card manufacturer suffered economic losses because the cost of each card is higher than 20 yuan, and the local government subsidized the company with 100 million yuan in 2008.

The official reply failed to convince Shi, and he repeatedly asked the Beijing Municipal Administration and Communications Card to publicize the information of its deposit fund annually, but his demand has not been met.

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