U.S. Rep. Marsha Blackburn believes a law that critics say provided less scrutiny of drug companies and distributors had unintended consequences and should be "addressed immediately," a spokesman said Monday.

The comment comes in light of a joint investigation by 60 Minutes and The Washington Post in which a whistleblower accuses the Tennessee Republican and other congressional lawmakers of lax scrutiny of drug companies and distributors.

The story, which was published Sunday, featured an interview with Joe Rannazzisi, who previously ran the U.S. Drug Enforcement Administration's Office of Diversion Control.

Rannazzisi, along with Jonathan Novak, a former DEA attorney, pointed to a bill sponsored by Rep. Tom Marino and co-sponsored by 14 others, including Blackburn, which they said stripped the federal agency of the ability to freeze suspicious shipments of opioids.

Prior to the legislation's passage in 2016, the DEA had been able to halt drug distributors from sending millions of opioids to doctors and pharmacies who law enforcement thought were feeding people addicted to opioids.

The sponsors of the bill previously said it was necessary in order to ensure patients had access to pain medicine.

In a statement provided to the USA TODAY NETWORK-Tennessee on Monday, a spokesman for Blackburn, who launched her Senate campaign Oct. 4, said, the congressman had a long history of fighting the opioid epidemic.

"If there are any unintended consequences from this bipartisan legislation — which was passed unanimously by the House, Senate and was signed into law by President Obama — they should be addressed immediately," the spokesperson said.

Earlier in the day, Sen. Claire McCaskill, D-Mo., said she will push new legislation to undo the 2016 measure, which was approved by both chambers of Congress and signed into law by then-President Barack Obama.

Also on Monday, Sen. Joe Manchin, D-W.Va., called for President Donald Trump to withdraw his nomination of Marino to serve as the lead of the Office of National Drug Control Policy, which requires Senate confirmation.

In addition to co-sponsoring the legislation, Blackburn received $120,000 in campaign contributions from the pharmaceutical industry, according to The Washington Post.

Blackburn initially declined to comment for the story. She did not immediately respond to a request for comment Monday morning.

The Washington Post and 60 Minutes investigation also noted that Blackburn and Marino wrote a 2014 letter in which they accused Rannazzisi of trying to "intimidate the United States Congress" while asking for an Inspector General's probe into Rannazzisi.

Back home, Blackburn, who is running for the U.S. Senate seat currently held by Sen. Bob Corker, has already been blasted by some.

► More: US Rep Marsha Blackburn launches Senate bid

“At the crucial time when she should have been protecting us, Rep. Blackburn championed a bill that imprisoned even more Tennesseans in a devastating cycle of drug dependence," said Mary Mancini, chair of the Tennessee Democratic Party, citing statistics on the number of overdose deaths in Tennessee in recent years.

Overdose deaths continue to rise in Tennessee, fueled in large part by both prescription and illicit opioids. In 2016, at least 1,631 died from overdoses in the state — a number that experts say is an undercount of the real toll.

"As a public servant, Blackburn's job is to protect Tennesseans from harm," Mancini said. "She's supposed to have our backs. Instead, she has sacrificed the most vulnerable of us for what she could get from powerful special interests.”

In a statement, James Mackler, an Iraq War vetehosran and Nashville attorney who is seeking the Democatic nomination for the U.S. Senate seat held by Corker, vowed to stand up to special interests and lobbyists.

"That Congresswoman Blackburn would champion legislation like this while Tennesseans face an opioid epidemic is all one needs to know about her priorities."

Last month, Tennessee Attorney General Herbert Slatery issued subpoenas and demand letters to pharmaceutical companies and distributors as part of a 41-state coalition’s investigation into “unlawful practices in the marketing, sale, and distribution of opioids.”

More: Opioid epidemic 'getting worse instead of better,' public health officials warn

Distributors AmerisourceBergen, Cardinal Health and McKesson were among those served with demand letters — all three companies were named in the 60 Minutes/Washington Post investigation.

Anita Wadhwani contributed to this report.