Insurance experts are urging Congress to decide how it will repeal and replace Obamacare by the end of March to give them enough time to set rates for next year.

"I think you need to provide some indication to plans as quickly as possible, but March would be helpful," Tennessee insurance commissioner Julie Mix McPeak told the Senate Health, Education, Labor and Pensions Committee Wednesday morning.

Insurers are anxiously awaiting what Republicans will do with the Affordable Care Act, which they have vowed to repeal. Companies are required under law to apply in May for selling on the Obamacare marketplaces and submit proposed rates mid-July for approval in August.

That timeline adds pressure on Republicans to decide on their strategy, or they could risk destabilizing the individual insurance market, leading to even more insurer exits and premium increases. GOP leadership has said a plan will be ready soon but haven't set a deadline.

"When do we have to act?" HELP Chairman Lamar Alexander asked insurance experts at a hearing Wednesday morning.

Marilyn Tavenner, president of the insurer association America's Health Insurance Plans, said insurers will find it hard to set 2018 rates for their plans if they don't know whether they will continue receiving subsidies through the healthcare law.

"The uncertainty around cost-sharing subsidies and the tax credits would cause them to hesitate to price," Tavenner told the panel.

Janet Trautwein, CEO of the National Association of Health Underwriters, also pointed to March as a key month for when insurers need certainty about what will happen with the healthcare law.

"I think the latest would be the end of March, with carriers having these filing requirements," Trautwein said.