PORTLAND, Maine » American fishermen are digging in for a fight over a proposal to shut down the vestiges of the U.S. harvest of shark fins, prized for soup and traditional medicine in Asia, and send a message to the rest of the world.

The traditional “finning” of sharks — in which they are pulled out of the water, have their fins sliced off and are discarded into the sea, often still alive but unable to swim — is already illegal in the U.S., but fishermen are still allowed to hunt sharks and have their fins removed during processing on land.

A bill backed by Sen. Cory Booker, a New Jersey Democrat, and others promises to ban the sale and possession of shark fins to ensure U.S. fishermen and seafood dealers no longer participate in the global fin trade. Supporters say the bill would close loopholes left open by measures passed in 2000 and 2010 to protect sharks.

“America can become a global leader by shutting down the domestic market for shark fins,” Booker said.

Fins from as many as 70 million sharks end up in the worldwide fin trade every year, and completely removing the U.S. from the industry would tell the world that it needs to stop, Booker said.

Lora Snyder, campaign director for the conservation group Oceana, has compared shark fins to the trade of elephant ivory and rhino horn. She said the legislation to ban the trade is a step toward saving sharks.

But some commercial shark fishermen and fish processors say the effort is wrongheaded and will harm industry more than it protects sharks. The U.S. shark fishery was worth about $2.5 million in 2014, Booker’s office said. The worldwide trade is worth hundreds of millions.

In the U.S., sharks are processed for their meat, as well as the fins, most of which are sold to Hong Kong. The U.S. also imported an annual average of 36 tons of dried shark fins from 2000 to 2011, according to Sen. Richard Blumenthal, a Democrat from Connecticut and a supporter of Booker’s legislation.

There are more than 400 permitted shark fishermen in the U.S., with the largest concentrations in Florida and Louisiana. Fishermen brought more than 600 metric tons of sharks to land in states from Maine to Texas in 2014.

Jeff Oden, a former North Carolina shark fisherman who left the business about 10 years ago to focus on other species amid mounting regulatory pressure, said the legislation is well intentioned but won’t stop international finning, and could actually increase pressure on sharks.

“Other countries that are less likely to be as sustainable as us will fill our void,” Oden said.

Shaun Gehan, a lawyer who represents shark fishermen, said the inability to sell fins would devastate the shark fishing business, which he described as conservatively managed already. Eleven states already have laws against the sale of shark fins, though shark fin soup can still be found on the menu in Chinese restaurants in many states.

American fishermen are allowed to harvest many different kinds of sharks, including tiger sharks, bull sharks and some species of hammerhead. Shark conservation group Shark Savers has said the 14 kinds of shark that are most prevalent in the international shark fin trade are all threatened with or near-threatened with extinction.

The bill would still allow fishermen to harvest sharks for their meat, though some in the industry say it wouldn’t be worth the cost of business, because much of the value is in the fins. There would also be an exception for smooth dogfish, which could still be used for fins.

The bill is pending in the Senate Commerce Committee, but no votes are scheduled. Booker introduced the bill along with Sen. Shelley Moore Capito, a West Virginia Republican, Rep. Ed Royce, a California Republican, and Gregorio Kilili Camacho Sablan, the Northern Mariana Islands delegate to Congress.