Some coastal towns are changing the way they license clam diggers in response to the U.S. Department of Labor’s concerns that they have been forcing diggers to do unpaid conservation work.

Officials in Harpswell and Brunswick are considering measures to increase the cost of commercial clam harvest licenses that would, at the same time, give diggers a discount if they participate in conservation efforts.

“It gives every individual the option to pay more or just help take part in our conservation measures,” said David Wilson, a clam digger who chairs Harpswell’s Marine Resources Committee, which has endorsed the proposal and plans to ask residents at Town Meeting in March to approve it.

The proposed measures would be similar to those adopted last year in Waldoboro and by the Frenchman Bay Regional Shellfish Committee, which manages the Frenchman Bay clam flats for seven towns, including Ellsworth.

Managers in Harpswell propose increasing the cost of a commercial clam license next year from $200 to $600. But diggers who take part in four conservation activities this year would pay the current $200. The activities include reseeding clam beds, collecting water quality samples, cleaning up the shore and attending conservation meetings.

A similar measure is being proposed this month in Brunswick, where diggers now must do 20 hours of conservation work annually to qualify for a license.

The Frenchman Bay Regional Shellfish Committee in July established a two-tier fee system – $580 for diggers who don’t do conservation work and $400 for those who do. Waldoboro last year began offering diggers the choice of a license for a “regular fee” of $210 or a “conservation fee” of $150 for those who do six hours of conservation work.

The issue initially emerged in Waldoboro in 2013 after a digger in that town filed a complaint with the U.S. Department of Labor charging that the town’s work requirement effectively made clam diggers unpaid town employees.

The DOL investigated the charge and concluded that the town was in violation of the Fair Labor Standards Act’s minimum wage requirements. However, it also concluded that reseeding clam beds is an exempted activity because it directly benefits the clam diggers.

In addition, the federal agency found that the town’s requirement that children under 16 who apply for youth clam-digging licenses take part in conservation work violated child labor laws.

Immediately, towns up and down the coast stopped enforcing work requirements for children applying for licenses, according to Denis Nault, municipal shellfish coordinator at the Maine Department of Marine Resources.

He said individual towns have been trying to figure out how to address the other issues raised by the Labor Department.

“There are options out there,” he said. “It’s really up to the towns to do that.”

The two-tier fee structure has another advantage: It’s easier to penalize diggers who don’t do conservation work, said Darcie Couture, the marine resource coordinator for Harpswell.

In the past, she said, revoking a license was the only option to penalize people who refused or forgot to perform their conservation work, she said, and managers were reluctant to take such drastic action, especially if it would affect someone’s ability to make a living.

Under the proposed new system, she said, managers would simply increase the license fee for people who don’t do the required conservation work.

There are between 1,600 and 1,800 people in Maine with commercial clam licenses; nearly 80 towns in Maine have issued them. Diggers in 2013 sold $17 million in clams, making it the third most valuable fishery in Maine, behind the elver and lobster fisheries.