The "Cut gift money for shark-fin banquets" campaign calls on netizens to tell couples about to get married to leave the traditional soup off the menu or receive a 30 percent cut in their red packets or money gifts.

Within days, 3,896 people signed up and more are joining daily.

Group originator Clement Lee Yui- Wah said he decided on the anti-shark's fin campaign after seeing a video clip in which hunters off the Philippines cut off the fins of a young whale shark and left it adrift to die.

Other fishermen saw its plight and towed it to shore so it could die faster. A Hong Kong tourist recorded it and put the clip online.

Lee, who's in his forties and works in the United States, said he will never eat shark's fin soup after seeing the video.

He called on Hong Kong people to change existing social traditions and pay more attention to animal protection.

"Shark's fin is not a must at wedding dinners. We need to develop a new culture under which eating shark's fin is considered shameful," he said.

Lee agreed one of the problems to be overcome is the traditional belief that a wedding banquet without shark's fin is an insult to guests. "This is totally wrong. We must push home the message that eating shark's fin is the same as committing a crime," he said.

Environmental protection group Oceana released a report last month that showed Hong Kong had imported more than 100,000 tons of shark's fin from 87 countries last year - making it the largest such importer in the world.

One reason for this is that more sophisticated fishing methods have reduced the cost, making shark's fin more affordable. This, in turn, has increased consumption, leading to even more fierce shark hunting.

"Not everyone has the power to stop the inhumane killing of sharks but everyone has the right to boycott shark's fin dishes," Lee said.

One Facebook user named Ida Ng wrote: "People enjoy their food without thinking of such cruel behavior." Another, Tsai Yongling, said: "Don't have shark's fin soup anymore."

Lee said the group also wants to encourage people to name organizations that include shark's fin in company dinners, lobby the catering business to offer alternative dishes, and lobby the Legislative Council to initially levy a 10 percent tax on shark's fin, increasing it to 200 percent within five years.