Publishing industry professionals have expresse d concern over a number of online promotions in which copyright ed e-books are being sold for free.

China's largest online bookseller Dangdang.com is in the middle of a sales effort that includes almost all of its e-books being sold for free, from Wednesday to Friday.

Rival Jingdong Mall, announced on Wednesday that it also will offer 50,000 e-books for free.

Some leading names in the industry said that someone will have to pay in the end, and a resultant price war between the industry's main players could be hugely destructive to the secto r.

According to local media , Chinese writer Feng Tang has already delivered a lawyer's letter to the retail ers protesting about the giveaways, which he says is costing him a considerable amount in lost royalties.

Zhao Chen, from People's Literature Publishing House, told Beijing News that the promotion will bring harm to companies.

Wang Qian, a professor at the Intellectual Property School, East China University of Political Science and Law, told China Daily: "It's legal if Dangdang has the authors' authorization and paid them for that."

Dangdang's senior PR director Guo He said that the promotion had been approved by the company's legal department.

But Guo refused to confirm or deny whether it gained the permission of all the authors and publishers before starting the promotion.

Guo said that if they got complaints from content providers during the three days, they would pull the relevant free products out of respect.

"Basically, we are doing this because we want to draw more people into reading books, especially copyrighted e-books," Guo said.

As well as free e-book downloads, Dangdang is also offering 50 percent off printed books, to "celebrate the upcoming World Reading Day", Guo said, while denying the promotion had anything to do with the possible launch of the company's own e-reader.

Guo said his company considers there are only a small number of regular e-book readers in China and encouraged publishers to invest more time and money in the future marketing and selling of e-books.

"We share the same ambitions as the writers and publishers ¡ª to increase the number of potential consumers," he said, adding the short-term sales expected by the promotions would not affect the interests of either groups over the long term.