"While are disappointed," the leaders wrote to former NECC President Barry Cadden, "the Committee must proceed with the investigation."
More than 20 people have died and about 300 have been sickened by fungal meningitis linked to NECC steroid injections.
Congress, now in recess, has been pushing for action on the outbreak for weeks.
The spate of illnesses has put focus on compounding pharmacies, which reprocess drugs on a large scale to fit patients' needs and are not obligated to follow many rules that apply to drug makers.
In a recent statement, Rep. Edward MarkeyEd MarkeyGreens slam Trump’s Interior Department pick Senate sends annual defense bill to Obama's desk Overnight Cybersecurity: Fed agency IT report cards | Senate Dems push for briefing on Russia hacks MORE (D-Mass.) accused the NECC of "masquerading as a compounding pharmacy so it could escape federal regulation when it was actually operating as a drug manufacturer."
"This company may have disregarded federal guidelines, and we need to know from [regulators] whether the company misled regulatory authorities and if sanctions against the company are available or warranted," said Markey, whose district houses the Framingham-based company.
Markey has promised a bill that will enable greater oversight of compounding pharmacies. Rep. Rosa DeLauro (D-Conn.) has introduced a similar measure, and Sen. Richard BlumenthalRichard BlumenthalOvernight Tech: AT&T, Time Warner CEOs defend merger before Congress | More tech execs join Trump team | Republican details path to undoing net neutrality Overnight Energy: Trump taps EPA foe to head agency | Energy reform bill officially dead CNN’s parent company promises to defend journalistic independence MORE (D-Conn.) recently called on the Justice Department to launch a criminal investigation of the NECC.
The outbreak has also prompted criticism of the Food and Drug Administration (FDA), which lawmakers claim failed to follow up with the NECC after past inspections prompted worries that the company's practices were unsafe.
Some of the NECC's violations directly foreshadowed the contamination of steroid injections linked to the current cases of meningitis, lawmakers wrote Monday.
"On December 4, 2006, the FDA sent the NECC a warning letter detailing significant violations of the Food, Drug and Cosmetic Act witnessed by the investigators," lawmakers wrote to an NECC lawyer, Paul Cirel.
"Included in the list of violations was the NECC's manipulation of a sterile injectable product, which caused the FDA to be 'especially concerned about potential microbial contamination,' " the leaders wrote.
The NECC has recalled all of its products and surrendered its state license in response to the outbreak, which has put an estimated 14,000 people at risk.
Monday's letter was signed by Energy and Commerce Committee Chairman Fred Upton (R-Mich.) and ranking member Henry Waxman (D-Calif.).
Reps. Cliff Stearns (R-Fla.), Diana DeGette (D-Colo.), Joe Pitts (R-Pa.), Frank Pallone Jr. (D-N.J.), Michael BurgessMichael BurgessPentagon's suppressed waste report only tip of the inefficient machine This week: Pelosi's test Trump calls for special session of Congress to repeal ObamaCare MORE (R-Texas), John Dingell (D-Mich.) and Joe Barton (R-Texas) also signed.
—This post was updated at 11:50 a.m.