Nonprofit groups that advocate treating pain with medications have received $65 million since 1997 from opioid manufacturers, according to a bipartisan congressional investigation.

The strategy was aimed at increasing sales of prescription painkillers, the Associated Press reports.

The report, from the Senate Finance Committee, found the opioid industry’s contributions to the groups continued in recent years, even as the nation’s opioid crisis gained greater attention. Committee co-chairs Senators Chuck Grassley of Iowa, a Republican, and Ron Wyden of Oregon, a Democrat, are considering legislation that would expand a federal system that tracks payments from companies to doctors to include payments to nonprofit groups.

“We’ve found that the possibility of donor influence could and has undermined the efforts to develop and advocate good policy,” Grassley said in a statement. “When it comes to opioids, we need to make sure there is transparency and accountability to prevent what, in this case, led to serious public misunderstanding of the risks of these highly addictive drugs.”