Fred Thompson says he "has no recollection" of lobbying on behalf of a family planning group.
The Los Angeles times reports that back in 1991 Thompson lobbied then President George Bush to relax a regulation that prevents federally funded clinics from offering abortion counseling.
Minutes of a 1991 meeting, cited by the Times, said Thompson had been hired to help in discussions with the president's office.
A spokesman for Thompson says it's "not unusual" for lawyers to be asked to give advice to colleagues for clients with whom they personally disagree.
But the former head of the National Family Planning and Reproductive Health Association says she specifically remembers discussing Thompson's lobbying work with him in phone conversations and during meals at Washington restaurants.
The former senator is weighing a Republican presidential bid as a social conservative.