Chao's email, and others related to deadline concerns about HealthCare.gov, were released by the House Energy and Commerce Committee, which has been conducting oversight hearings into the tech-troubled website.
HealthCare.gov's many software issues have seriously affected enrollment in Obamacare insurance, with just 27,000 or so people signing up from 36 states in the first month of operation. The Obama administration is engaged in a round-the-clock effort to fix the site.
But its dismal performance to date spurred President Barack Obama on Thursday to allow insurers who had been canceling people's policies because they did not comply with the Affordable Care Act to continue with those policies for the next year.
Committee Chairman Fred Upton, R-Mich., said of the memos, "Administration officials looked us in the eye and told us everything was 'on track' but when we pull back the curtain now, the mess is disturbing."
"What reason do the American people have to believe that the administration is capable of meeting its Nov. 30 goal for fixing HealthCare.gov or its Jan. 1 promise to deliver health care to Americans across the country," Upton said. "The botched rollout has created a serious question of competence and trust in the administration that we will continue asking at our hearing next week."
A CMS spokeswoman, in a statement Friday, said: "This email discusses one small piece of ongoing discussions about managing deliverables and communicating expectations that were on a short timeline to meet Oct.1. Management concerns about meeting timelines are expected for any project of this size and scope."
(Watch: Florida Blue CEO: We'll work on Obamacare insurance fix)
"The federal marketplace is comprised of distinct pieces of functionality that, together, make up the full integrated system—plan management, eligibility and enrollment and financial management. CMS prioritized essential functionality to be live on Oct. 1 to ensure that consumers would be able to apply for eligibility and select a plan. Other functionality will come online over time. This is a complex project with a short timeline—and as such issues were prioritized to meet the Oct. 1 launch date."