A security guard at the National September 11 Memorial and Museum and a Florida man face firearms trafficking charges after selling more than 25 guns — including a MAC-10 machine pistol — to an undercover officer, the authorities said on Friday.

The security guard, Maquan Moore, 29, of Manhattan, allegedly conspired with Morris Wilson, 32, of Orlando, to sell the guns. Prosecutors say Mr. Moore sold several guns to an undercover officer in Lower Manhattan, and that Mr. Wilson brought some of the weapons to New York from Florida.

Each faces multiple counts related to the movement, transportation and receipt of firearms. If convicted of all counts, Mr. Moore would face a maximum penalty of 30 years in prison; Mr. Wilson would face 15 years.

Lawyers for the two men could not immediately be reached on Friday.

The men “are responsible for illegally introducing into Manhattan scores of illegal firearms — including assault-style weapons capable of inflicting mass casualties — and knowingly doing so in the neighborhood of a nearby school,” Geoffrey S. Berman, the United States attorney for the Southern District of New York, said in a statement on Friday. “Their alleged disregard for public safety could have had catastrophic consequences. The danger of selling unlicensed firearms cannot be overstated.”