Several members of the Iron Horsemen Motorcycle Club in Maine, including the owner of the group’s clubhouse in Old Orchard Beach, have been indicted on federal drug conspiracy charges following a yearlong investigation.

Federal and local law enforcement agents made 16 arrests over the past two weeks, and they are still looking for three others named in the indictment, which was unsealed on Thursday.

Agents seek to arrest Richard W. Szpyt of Haverhill, Mass., Michael Balot of South Portland and Robert Boothby of Monson.

Most of the alleged conspirators live in Old Orchard Beach, Limerick or other towns in York County, according to court documents. Of the defendants who have been arrested, five are in federal custody, 10 posted bonds and have been released, and one was released on personal recognizance.

York County Sheriff Maurice Ouellette said his office initiated an investigation about a year ago, and as the large scope became apparent he turned over the lead role to the U.S. Drug Enforcement Agency and the U.S. Bureau of Alcohol, Tobacco and Firearms.

Federal officials declined comment today.