President Barack Obama is telling workers and volunteers signing up customers for health insurance coverage that the enrollment season comes at a critical time in the Affordable Care Act's history.

In a conference call, Obama is challenging workers to ensure the insurance program is in a position of strength when the next president comes into office.

Obama's call with thousands of stakeholders comes with open enrollment beginning Tuesday and as his signature health care law comes under attack ahead of Election Day.

Some insurers have bailed out of markets and premiums are jumping in many states.

But Obama says government tax credits will offset the premium increases for most consumers. He sayspeople will be pleasantly surprised at just how affordable their options are, if they shop around.