BOSTON – Nearly two dozen members of Congress are asking the U.S. Department of Commerce secretary to increase fishing catch limits before the Northeast switches to a new management strategy.

Under the new system, in effect May 1, fishermen working in groups called “sectors” will be allowed to catch a certain amount of each species of groundfish, such as cod and flounder. If the sectors exceed their limits on any species, they must stop fishing for all species.

In the letter to Commerce Secretary Gary Locke dated Wednesday, the lawmakers said catch limits for some fish, such as pollock, are so low that fishermen could exceed their sector’s limit in one tow of their nets.

They asked for catch increases, especially in these so-called “choke stocks,” to prevent that.

“We cannot expect fishermen to operate in an environment where quite literally the first tow they make could be their last,” the letter reads.

The letter, signed by 23 senators and representatives, said Locke should use his emergency authority so the new system doesn’t collapse before it has a chance to work.

Massachusetts Democratic Rep. Barney Frank, who signed the letter, said the coming switch “is a controversial step that will cause some turmoil in the fishing industry under the best circumstances. Increasing the catch limits would reduce this turmoil.”

The Department of Commerce did not immediately return a request for comment.

Marjorie Mooney-Seus, a spokeswoman for the National Marine Fisheries Service, said the agency “will consider the recommendations from Congress carefully and will respond to them directly.”

Julie Wormser of the Environmental Defense Fund said she supports lawmakers’ efforts to help fishermen, and added regulators should always work to update stock estimates — as they now are with pollock — so catch limits aren’t set too low.

But she cautioned against allowing more fishing on stocks that need protection.

“If these stocks really are overfished, and you increase the catch limits, you make the problem worse next year,” she said.

The current system tried to stop overfishing by making fishermen less efficient, such as by limiting their days at sea or forcing them to use gear that allows smaller fish to escape. But federal fishery managers say key stocks are still overfished, even as some fishermen have been limited to just 24 fishing days annually.

The switch to the “sector” system aims to give fishermen more autonomy and opportunity to make money while protecting fish stocks with strict catch limits.

But some fishermen say federal estimates wildly undercount the fish, and that the amount of fish allotted to their sectors is far too little to make a living.

Another frustration is that the rules have forced fishermen to stop catching abundant species, such as haddock, to protect the vulnerable species that swim among them.