The U.S. attorney's office in Bay City says 73-year-old Russell Hesch of West Branch and his son, 50-year-old David Hesch of Loveland, Colo., have been arrested.
Court documents say Stupak's office in Menominee received a letter May 25 that threatened the congressman and his wife and son.
An attorney for Russell Hesch says his client is not guilty.
Stupak was spokesman for about a dozen House Democrats who withheld their support for the health bill because they wanted assurances it would not allow federal funding of abortions.
He ultimately voted for the bill in March after reaching a deal with the White House and Democratic leaders.