Two Senate Democrats have asked CMS and HHS to make a last-minute extension of the open enrollment period for the Affordable Care Act (ACA)’s insurance exchanges, arguing the Dec. 15 deadline will leave too many interested customers either without health coverage or automatically enrolled into plans which “may no longer be the best choice for their families.”

In prior years, under the Obama administration, open enrollment lasted until Jan. 31. The Trump administration proposed first proposed in February cutting that enrollment period in half, wrapping up on Dec. 15. On a week-by-week basis, plan selections on the exchanges are higher than in 2016, but with customers having less time to pick their coverage, total enrollment will likely decrease.

Sens. Ron Wyden, D-Oregon and Patty Murray, D-Washington, asked in a letter to CMS and HHS to extend the open enrollmeent deadline to Jan. 31, 2018. They argued the shorter enrollment period is “compounded” by other administration efforts to “destabilize the insurance market,” such as halting cost-sharing reduction subsidies for insurers, cutting funding for navigators to help people select coverage and a 90 percent reduction in the advertising budget for the ACA—which may mean customers don’t know they have to sign up for coverage earlier this year.

“Since the very beginning of the open enrollment period, HHS has done virtually nothing to promote enrollment and notify customers about this severe cut to open enrollment's timeline or the vast differences from the previous year’s offerings,” Murray and Wyden wrote.

The senators argued the shortened enrollment period would impact insurers. Past enrollment patterns have shown young, healthier customers tend to sign up in larger numbers at the end of January as open enrollment winds down. If those customers don’t sign up this year, insurers will have to deal with an older, sicker risk pool on the exchanges.

In prior years, the Obama administration had pushed back the deadline for enrollment by a few days, as have some state-based exchanges. There’s no precedent, however, for such a long extension on such short notice.

“The deadline for people to shop and pick a plan for the upcoming year is December 15,” a CMS spokesperson said in a statement. “We continue to encourage people to make plan selections by that deadline so that their coverage can begin on January 1.”