Manchin cited Marino's support for the bill, which he said made it "significantly harder" for the DEA to bring enforcement against drug companies in cases of prescription painkillers being diverted from proper use.
"His advocacy for this legislation demonstrates that Congressman Marino either does not fully understand the scope and devastation of this epidemic or ties to the industry overrode those concerns," Manchin wrote the president.
Senate Minority Leader Chuck Schumer, D-N.Y., on Monday said, "I am calling on President Trump to withdraw the nomination of Representative Marino," NBC News reported.
"Confirming Rep. Marino as our nation's drug czar is like putting the wolf in charge of the hen house," Schumer said.
"The American people deserve someone totally committed to fighting the opioic crisis, not someone who's labored on behalf of the drug industry," Schumer said, according to The Washington Post.
Marino's spokesman did not return a request for comment from CNBC.
In 2015, more than 33,000 people died from either prescription opioids, heroin or fentanyl, a synthetic opioid, according to the federal Centers for Disease Control and Prevention.
In its story Sunday, The Washington Post wrote:
In April 2016, at the height of the deadliest drug epidemic in U.S. history, Congress effectively stripped the Drug Enforcement Administration of its most potent weapon against large drug companies suspected of spilling prescription narcotics onto the nation's streets.
By then, the opioid war had claimed 200,000 lives, more than three times the number of U.S. military deaths in the Vietnam War. Overdose deaths continue to rise. There is no end in sight.
A handful of members of Congress, allied with the nation's major drug distributors, prevailed upon the DEA and the Justice Department to agree to a more industry-friendly law, undermining efforts to stanch the flow of pain pills, according to an investigation by The Washington Post and "60 Minutes." The DEA had opposed the effort for years.
The law was the crowning achievement of a multifaceted campaign by the drug industry to weaken aggressive DEA enforcement efforts against drug distribution companies that were supplying corrupt doctors and pharmacists who peddled narcotics to the black market. The industry worked behind the scenes with lobbyists and key members of Congress, pouring more than a million dollars into their election campaigns.
The chief advocate of the law that hobbled the DEA was Rep. Tom Marino, a Pennsylvania Republican who is now President Trump's nominee to become the nation's next drug czar. Marino spent years trying to move the law through Congress. It passed after Sen. Orrin G. Hatch (R-Utah) negotiated a final version with the DEA.