CNN

Documents show Thompson lobbied for an abortion rights group.

WASHINGTON (CNN) - It looks like an old job could spell new trouble for probable presidential hopeful Fred Thompson.

During his run up to a probable bid, Thompson has expressed opposition to abortion. He told a conservative group last month that he holds a "belief in the sanctity of human life." And when he officially jumps into the race for the White House, he's counting on the support of values voters.

But billing records show that in 1991 and 1992, Thompson spent some 20 hours lobbying for a group that was trying to ease federal laws that restricted abortion counseling. The records detailing his work for the National Family Planning and Reproductive Health Association were first reported Thursday by the New York Times and also obtained by CNN.

According to the records, Thompson lobbied the administration on three separate occasions for the abortion rights group. He billed them for over $5000 in legal services and spent the bulk of that time on conference calls with the group's president.

After the Los Angeles Times broke the story earlier this month, Thompson said he didn't remember dealing with the group. And despite these records surfacing, a Thompson spokesman stuck by his story.

“Senator Thompson has no recollection of doing work on behalf of this group," spokesman Robert Traynham said. "It is not unusual for a lawyer, when asked by a colleague, to provide counsel or assistance when asked, including on matters on which they personally disagree."

Thompson's already feeling the heat. A posting on YouTube shows his answer in a 1994 Senate debate to a question about supporting or opposing abortions on demand, where he said, "I do not believe that the federal government ought to be involved in that process."

But Thompson's voting record in the Senate was consistently anti-abortion. So will the right give him a pass on this current controversy? Political analyst Stu Rothenberg thinks so. "The conservative wing of the Republican Party really wants to be able to support somebody and because of that they may be able to move past this," he said.

–CNN's Lauren Kornreich and Paul Steinhauser