He said Lee Swartz, a Shuster campaign attorney, told him a hearing might mean subpoenas for "many of my signers and supporters."
"Second, I was being threatened with the possibility of being assessed for all or part of Shuster's legal costs if I fought the challenge and lost," Politis said.
Politis said he plans "a full-blown write-in campaign for the Democratic nomination for Congress" in the 9th District.
As for claims he forged signatures, Politis said he "transferred" three valid signatures from two petitions to another petition. He said he did so to save petition circulators from having to get them notarized.
He said Shuster's campaign accused him of falsely swearing he circulated petitions.
"The largest of these was one placed on a desk for several days at the Waynesboro Golf Course," he said.
Politis said it was set out for any registered Democrat to sign and he "took responsibility for the signatures and had it notarized."
Politis said he collected about 700 of the signatures and supporters collected the rest. He said his campaign didn't have "the time or the financial resources to research each signature against the latest records."
Politis said he believed he had more than the 1,000 valid signatures required to get on the ballot.
"Do you accept anybody?" Doug Harbach said Monday night. A former Democratic candidate for Franklin County Clerk of Courts and Greene Township supervisor, Harbach said he'd heard about irregularities in Politis' petitions.
"I approached the Shuster campaign to see the documents and see if what I heard from Democrats and some Republicans was true," Harbach said.
"I signed a verification of the truthfulness of the petition that was filed in Commonwealth Court," Harbach said of his role in the court challenge.
"I don't think Doug should be speaking out for the Democratic Party. I think that should be left to the voters," Franklin County Democratic Chairman William Butts said Monday.
"The allegations against Bud Shuster, if proven, would be more serious than the problems Paul has with his nominating petitions," Butts said.
Shuster, chairman of the House Transportation and Infrastructure Committee, has been the subject of investigations by the House Ethics Committee, but has not been charged with any wrongdoing.
"People who live in glass houses shouldn't throw stones," Butts said.
Shuster, running for his 14th term, faces a challenge in the Republican primary from Monte Kemmler of Mifflin County. Kemmler was the Democratic nominee in 1996 and lost in a landslide to the incumbent.