Victims campaigner Willie Frazer has claimed a car load of thugs arrived at his home twice this week as he spoke up for the victims of the Kingsmill Massacre.
He also said he and his office had received 50 abusive phone calls in a single day, and had received a threatening email warning him to stop his work.
The huge spike in intimidation followed the Kingsmill controversy.
"I am regularly at the receiving end of threats but there has been a massive spike in the last couple of days," he said. "Usually it doesn't bother me too much, but when a car load of men turns up at your house twice in one day, that's something to worry about."
Mr Frazer said he was especially worried about the intimidation impacting on his family.
"They arrived at the office shouting abuse, and that's one thing. But to go to my house is a step up," he said. "We don't know what they were planning to do. It's worrying."
The PSNI said it is investigating reports that a number of threatening phone calls and an email have been received.