"I will not support him because he's a dishonest person and that's my bottom line," Mannix told the Politico. "I cannot support a dishonest campaign. I need to stick to my principles here, and he'll have to deal with it. That doesn't mean I'm endorsing or supporting the Democrat, but I'm not doing anything for him."
Erickson defeated Mannix by a four-point margin, 49 to 45 percent in what was a bitter primary campaign largely defined by Mannix's allegations that Erickson paid for an ex-girlfriend's abortion nearly a decade ago.
Erickson has said he was unaware his ex-girlfriend was pregnant, though he acknowledged giving her $300 and dropping her off at a doctor's office for an appointment.
Despite the primary loss, Mannix still carries considerable clout within the conservative community in Oregon. Mannix carried the district in his two unsuccessful statewide runs for governor and attorney general.
The state's leading pro-life group, Oregon Right to Life, has also said it will not be endorsing Erickson in the general election.
Erickson will be facing Democratic state senator and veterinarian Kurt Schrader in November's general election.