A. Barry Rand, chief executive officer of the AARP, sent the letter in advance of a scheduled vote on legislation to repeal the Affordable Care Act.
"We respect that there are those who do not support the Affordable Care Act, AARP opposes repeal because the new law includes many vital provisions important to older Americans and their children," Rand wrote.
"Through outreach and conversations with AARP members and other Americans, as well as information reflected in public polling, we have learned that older Americans and their families -- while still unclear on many aspects of the new law -- support key provisions of the ACA."
The AARP says seniors support:
-- Lowering drug costs for seniors in the Medicare Part D coverage gap or "doughnut hole" and adding free preventive services such as a yearly checkup.
-- Stopping insurance companies from canceling or pricing someone out of coverage if they get sick, denying coverage based on a pre-existing condition and cracking down on discriminatory practices that allow premiums be based on a person's age.
-- Capping out-of-pocket costs for individuals and families.
-- Allowing young adults up to age 26 to stay on their parents' insurance policies.
-- Giving seniors new options for receiving more cost-effective care at home.
Notable deaths of 2014 [PHOTOS]