A Texas volunteer search-and-rescue outfit grounded by federal regulators is fighting back, suing the government that maintains that its humanitarian efforts are illegal.

Federal Aviation Administration officials in February grounded Texas EquuSearch Mounted Search and Recovery Team, which deploys five-pound styrofoam drones to find the missing—all for free.

"There is no legal basis for the FAA to prohibit the operation of model aircraft for volunteer search-and-rescue activities," Brendan Schulman, the nonprofit's lawyer, wrote in the lawsuit Monday (PDF).

EquuSearch, which does not charge for its services, says it has found more than 300 persons alive in some 42 states and eight countries.

The FAA banned the commercial use of drones in 2007.

Last month, however, a judge ruled that the FAA's ban on the commercial use of drones was not binding because flight officials did not give the public a chance to comment on the agency's rules. Congress has delegated rule making powers to its agencies, but the Administrative Procedures Act requires the agencies to provide a public notice and comment period first.

The FAA said the search-and-rescue group could contract with a government agency and apply for a so-called "Certificate of Authorization" on a case-by-case basis. Approval, the agency said in an e-mail, is "sometimes in a matter of hours."