CMS - which operates within the US Department of Health and Human Services - has a policy of selecting a roster of preferred agencies, and will hear pitches from these companies.
Its incumbent agencies are Ketchum, Ogilvy PR Worldwide, GCI Group and American Education Development.
The quartet of firms - and others that want to bid - have until 10 June to submit proposals. CMS expects to award the contract in September.
The brief, which is capped at around £9.4m for the five-year period, involves media relations, research, message development, social marketing, education and training.
Although the number of agencies to be hired has yet to be determined, CMS said it wanted to appoint 'at least three'.
A priority for CMS will be to boost awareness of reforms mandated by the 2003 Medicare Modernization Act.
Although the selected agencies will get a chance to work on related campaigns, CMS plans to issue additional requests for proposals for the bulk of that work, said contracting officer Jaime Galvez.
CMS's external relations projects also include working with state health insurance assistance programmes and distributing an annual 'Medicare & You' booklet.
