Rae Tyson, a spokesman for N.H.T.S.A., said "it is highly unusual" for the agency to hold such a hearing to enforce safety regulations, saying he could not remember the last time such a hearing was held. Mr. Tyson said millions of dollars in fines could result.

The company is Transportation Collaborative Inc. of Warwick, N.Y., which does business under the name Trans Tech Bus. The company makes small buses using the underpinnings purchased from automakers such as Ford and General Motors.

In 2007, Transportation Collaborative purchased the assets of U.S. Bus of Suffern, N.Y., which was being pursued by the agency when it went out of business. N.H.T.S.A. asserted that U.S. Bus failed to carry out at least 15 recalls.

Now, the agency says T.C.I. must fix the vehicles because it appears that the new company is simply the old company with a different name.

"T.C.I. and U.S. Bus have continuity of ownership, management, personnel assets and general business operations," the agency said. The major shareholders are also the same, the agency says in its notice explaining why it had decided to hold the hearing.

Dan Daniels, the president of Trans Tech, declined to comment, but provided a written statement that says T.C.I. does not consider itself the successor of U.S. Bus, however, it will work with the agency to resolve the problem. The statement said that, "T.C.I. will continue to meet and exceed N.H.T.S.A.'s safety standards and ensure the well-being of its passengers."

The agency recently issued an advisory aimed at those who purchased the buses, noting the continued existence of "potentially dangerous safety defects" and recommending owners check a list of affected vehicles.

Often automakers inform N.H.T.S.A. when they find a safety issue. However, the agency's testing programs discovered the most serious problems with the buses. They ranged from body panels that do not meet the minimum strength to prevent "the structural collapse of a school bus body during a crash" to mounting bolts that "could fail to retain the seat, allowing the passenger to be thrown forward, possibly resulting in personal injuries."

The hearing is scheduled for Oct. 23 in Washington.