House and Senate Republicans are launching a series of investigations into the botched debut of ObamaCare's exchanges.
Republicans on the House Energy and Commerce Committee sent inquiries to contractors involved in the project on Thursday.
And in a joint effort, House Oversight Committee Chairman Darrell Issa (R-Calif.) and Sen. Lamar Alexander (R-Tenn.), the top Republican on the Senate Health Committee, sent a barrage of questions to Health and Human Services (HHS) Secretary Kathleen Sebelius.
The Obama administration is working to fix the problem, and reminding users they have six months to enroll in the new marketplaces.
Federal health officials are also cheering the millions of site users as evidence that patients are hungry for coverage under the healthcare law.
Last week, GOP lawmakers pounced on the healthcare.gov problems and criticized the Obama administration for failing to release real-time enrollment numbers.
Now, GOP-led committees are asking what went wrong.
The Energy and Commerce panel sent letters Thursday to Sebelius and key contractors behind the exchanges, including CGI and Quality Software Services Inc.
The inquiries sought documents, briefings with all parties within one week, and all communications between contractors and the HHS since the end of September.
"We're seeking information," Energy and Commerce Committee Chairman Fred Upton (R-Mich.) told The Hill. "Whether that leads to a hearing or not, we'll see. We're interested, though."
"There appear to be some major design problems. What I want to find out is: is this salvageable, how did this happen and when did they know about it?" said Rep. Tim Murphy (R-Pa.), chairman of the Energy and Commerce subcommittee on Oversight and Investigations.
Letters from the committee also went to Booz Allen Hamilton, eHealthInsurance, Equifax and Serco.
An analysis released Thursday by the Sunlight Foundation found that ObamaCare contractors like Booz Allen wield serious influence in Washington.
It is unclear exactly how many companies were involved in the exchanges' rollout, though it could easily be a dozen or more.
Other lawmakers have expressed interest in conducting oversight on healthcare.gov but say the government shutdown has staff juggling too many projects simultaneously.
—This post was updated at 6 p.m. to note the letter from Issa and Alexander.