Their complaint: The fee could deter people from registering their drones and, perhaps, reduce demand for them, according to drone industry groups.

“The $5 fee to cover administrative costs may prevent users from registering for both convenience and cost, especially in the case of small toy-like UAVs [unmanned aerial vehicle],” said a statement from the Small UAV Coalition, a drone advocacy group that includes Amazon (AMZN), Google (GOOG), and drone manufacture DJI.

After weeks of deliberation, the U.S. Transportation Department and the Federal Aviation Administration came out with a new policy requiring hobbyists to register their drones. Failure to do so could result in $27,500 fine, with criminal penalties reaching as high as $250,000 and three years in prison.

U.S. Transportation Secretary Anthony Foxx applauded the new rules and said in a statement, “Registration gives us an opportunity to work with these users to operate their unmanned aircraft safely.”

Lawmakers are increasingly concerned about a incidents and accidents caused by flying drones in dangerous or restricted areas. For example, a drone crash-landed at the U.S. Open tennis tournament in September, causing significant hand wringing by law enforcement but no injuries.

Although many drone advocacy groups and drone manufacturers helped the DOT and FAA create the new registration system, some of the groups involved expressed concerns. The mandatory registration fee was a particular sore spot.

The National Business Aviation Association, an aviation industry advocacy group and a member of the registration task force, said in a statement that more people would register if it was free.

“Given the agency’s stated goal that the registration process should serve primarily to educate [operators of small drones], we feel that process should be as inclusive as possible,” Sarah Wolf, a senior manager for security and facilitation for NBAA, said in a statement.

Doug Johnson, a vice president of technology policy for the Consumer Technology Association and a member of the registration task force, called the registration fee a “drone tax.”

“We all felt that having a fee-based system as opposed to something that was free could hamper the registration system,” Johnson said. Adding “at least a step or two” in the registration process might dissuade people from signing up, even in the face of penalties, he said.

Additionally, the registration fee, no matter how minute, risks dissuading people from buying drones, Johnson said. Even a “small amount could influence a decision,” he argued.

Johnson is also concerned that states and local governments are considering their own registration systems that would end up requiring people to register multiple times. The registration process could end up “messy and misaligned” with state rules undercutting federal rules, he said.

The Small UAV Coalition echoed Johnson’s concerns in a November letter to the FAA that said, “State and local governments have no authority to govern or regulate the operation of aircraft, both manned and unmanned, in the National Airspace System.”

Anne Swanson, an attorney who specializes in drone regulatory issues for the Cooley law firm, said the drone registration fees are a legal requirement. The FAA, like many government agencies, must charge a fee to deliver a service, even if hobbyists and businesses disagree.

“An agency can’t waive a statutory requirement,” Swanson said.

Although many of these drone advocacy groups differed with the FAA and DOT on the finalized registration process, Swanson said a number of groups banned together and agreed to be on the registration task force to “forestall more serious and tighter regulation from the Hill.”

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Dec. 15, 12:3o pm: This story updated to clarify that many federal agencies must collect fees.