The Obama administration issued new rules Tuesday that require insurance companies to cover people with preexisting medical conditions — one of the most popular provisions of President Obama’s healthcare law.

The Health and Human Services Department also began to implement other popular, but expensive, parts of the Affordable Care Act.

Regulations released Tuesday will prohibit insurers from charging women a higher premium than men, and will require plans in every state to cover certain services.

The regulations still leave key questions unanswered, including the structure of a federally run insurance exchange in the roughly 30 states that won’t set up their own. HHS officials said more information on the federal exchange will be coming soon.

“I’m confident states will have what they need to move forward,” HHS Secretary Kathleen Sebelius told reporters Tuesday.