Del. Kirill Reznik, who chairs the House of Delegates subcommittee on health, urged Hogan to weigh in directly with Republican President Donald J. Trump and emphasize the state's interest in preserving large parts of the law known as Obamacare.
Reznik told Dennis R. Schrader, secretary of the Department of Health and Mental Hygiene, that other governors — including Republicans — have urged the new administration not to make changes that would drop their states' citizens from insurance rolls.
Trump and congressional Republicans have vowed to repeal the law. While they have talked about replacing it, they have not reached consensus on what that would look like. Trump said in an interview with ABC News this week that he wants "to take care of everybody."
Hogan has defended a Medicaid expansion under the Affordable Care Act in letters to some congressional leaders and members of Maryland's delegation.
The governor has also said he does not want to see any Marylanders lose health coverage because of repeal.
Reznik, a Montgomery County Democrat, said that's not enough. He criticized Hogan for failing to take his concerns directly to the White House.
"Without the governor's advocacy on this, we are either going to be facing the likelihood of about a half-million Marylanders losing their coverage or having to come up with $3 billion a year to keep their enrollment," Reznik said.
Hogan wrote a letter dated Jan. 13 to House Majority Leader Kevin McCarthy and Senate Finance Committee Chairman Orrin Hatch, both Republicans, extolling Maryland's performance under the Affordable Care Act.
"Maryland continues to be a leader in health care coverage, with nearly 94 percent of our residents insured," the governor wrote. "Our uninsured rate decreased from 10.2 percent in 2013 to 6.6 percent in 2015."
Hogan told the lawmakers that over 260,000 Marylanders have health care coverage as a result of Medicaid expansion and another 150,000 have insurance plans purchased through the individual markets set up under the law.
The governor urged that any changes to the Affordable Care Act retain the provisions of Maryland's All-Payer model, the successor to the state's unique Medicare waiver that dates back to the 1970s.
The model has been credited with holding Maryland's health care costs down. Hogan suggested that Congress look at the plan as a "nationwide model."
Reznik said Hogan's letter didn't go far enough in defending the broader law and wasn't addressed to the right people. He noted that neither McCarthy nor Hatch is the top leader of his chamber.
"He's not doing anything with the White House," Reznik said. "It seems like he's trying to toe a line between quietly advocating in a haphazard way and not seeming as if he's coming out for Obamacare."
Schrader declined to comment, but Hogan spokesman Doug Mayer had a sarcastic reply to Reznik's criticism.
"He's a frequent critic of the governor on Twitter, and we appreciate his support," Mayer said.
The spokesman said the governor told the Maryland delegation Monday that he wants to preserve the state's waiver and make sure no Marylanders lose their insurance. He also addressed the Affordable Care Act in a news conference this week.
"We want to protect the good parts of the Affordable Care Act and we want to get rid of the bad ones," Hogan told reporters.
Mayer also said the administration's Medicaid director, Shannon McMahon, met with Trump's transition team on the waiver and the Affordable Care Act within the past month.
Hogan is in a potentially awkward position when it comes to addressing his concerns directly to the White House.
He was a conspicuous holdout among Republican governors in supporting Trump after he won the party nomination. Hogan said he wrote in the name of his father, former Rep. Lawrence J. Hogan Sr., for president.
Since Trump's election, Hogan has bristled at questions about his relations with the White House — at one point calling the questions stupid. The governor has not talked to Trump on the phone since the election, nor has he written to him on the Affordable Care Act.
The Los Angeles Times contributed to this article.