Jonathan Blum, a key U.S. health official in the U.S. Centers for Medicare and Medicaid Services (CMS) has resigned. This, according to an internal CMS memo reported on by Reuters.

Blum was the principal deputy administrator and Medicare director for the CMS. During his five years in the position he oversaw major reform initiatives, including the Affordable Care Act (ACT, also known as “Obamacare”). His final day at the CMS will be May 16.

The internal memo was written by CMS Administrator Marilyn Tavenner, who heavily praised Blum’s work at the agency. She specifically cited Blum’s initiative to bring competitive bidding for medical supply purchases to Medicare.

Though the specific reason for Blum’s departure has not been announced, the move could be related to two recent failed CMS initiatives. Blum was involved in proposed changes to both Medicare Advantage payments to private health insurers and changes to Medicare Part D prescription drug coverage.

The Part D proposal caused fears that some Part D drug coverage plans could be eliminated. Congressional leaders of both parties seized on the issue, claiming that seniors could lose coverage for necessary medications. Blum was the face of the proposal, testifying before a congressional subcommittee that, “In order for Part D to remain successful, we have to celebrate its successes and address its vulnerabilities.”

Tavenner’s memo stated that Blum will be pursuing “new opportunities.” The controversy surrounding the recent proposals was not mentioned.

Blum’s resignation comes just days after the higher-profile resignation of Health and Human Services Secretary Kathleen Sebelius. Though Sebelius denied that she was forced out of the position, her resignation comes just six months after the notoriously messy launch of the ACA’s health marketplace provisions. Sebelius and her administration were widely blamed for the Healthcare.gov website difficulties seen during the site’s first month of operation. Sylvia Mathews Burwell, current director of the White House Office of Management and Budget, has been chosen to replace Sebelius.

Image via CMS