A consumer group has sued the health insurer Aetna, claiming that it discriminated against patients with H.I.V. when it required them to obtain medications exclusively through its own mail-order pharmacy.

The lawsuit, filed Friday in federal court in San Diego by the advocacy group Consumer Watchdog, argues that Aetna’s policy violates the new federal health care law, which prohibits insurers from discriminating against people based on medical condition.

The company’s new policy, which takes effect Jan. 1 and applies to people who have purchased individual coverage, also raises the out-of-pocket amount that patients must pay for their treatments, potentially doubling it in some cases, according to the suit.

“We are in an era where presumably we guarantee access to health insurance to anyone, regardless of their health history or disability,” said Jerry Flanagan, the lead staff lawyer for Consumer Watchdog. But “insurance companies are still in the business of insuring people for the highest premium they can, and keeping their medical expenses down.”

In a statement, a spokeswoman for Aetna said the policy change was “part of our ongoing strategy to do all we can to keep our health plans affordable and help with medication adherence.” She said the move was consistent with industry standards.

Aetna is the most recent insurer criticized for its coverage of specialty drugs like H.I.V. treatments, which can cost more than $2,000 a month. In an effort to limit their exposure to the rising costs, many insurers have been placing additional restrictions on the drugs or increasing the out-of-pocket amounts that patients must pay.

In May, two consumer groups filed a federal complaint asserting that four insurers in Florida (including CoventryOne, an Aetna subsidiary) had discriminated against people with H.I.V. by making their drugs more costly and difficult to obtain. All of the companies have since agreed to make changes that would lower the cost of the drugs.

Consumer Watchdog has previously sued two other insurers, United Healthcare and Anthem Blue Cross of California, over similar policies restricting H.I.V. drugs to mail-order programs. Both of those cases were later settled and members of those plans can now opt out of the mail-order plans.

Aetna said members could opt out of its new policy as well. But the lead plaintiff in the lawsuit, who is not named for privacy reasons, claims in the suit that his requests to do so were turned down multiple times.

Mr. Flanagan of Consumer Watchdog said no such option was made available to consumers he had spoken to, and he asked Aetna to suspend its mail-order policy “to give us time to make the program truly optional.”

The federal government is also assessing the mail-order issue. This fall, the Department of Health and Human Services proposed a rule that would require insurers to offer an alternative to mail-order pharmacies, although members could be charged more for using a local retail pharmacy.

The department said that requiring consumers to use mail-order pharmacies could discriminate against people without a fixed address, or those who wished to keep their conditions confidential from neighbors or co-workers who might see the packages. The department has not said whether it will go forward with the proposed rule.

Insurers and pharmacy-benefit managers for years have been prodding consumers with chronic medical conditions to obtain their drugs through mail-order pharmacies.

Besides serving as an added revenue stream, mail-order pharmacies keep down costs as well as premiums, the industry claims. Compared to a neighborhood pharmacy, specialty mail-order pharmacies can also keep better track of the needs of patients with serious medical conditions, the industry says.

“People love it — they love the convenience and the savings and the ease of handling,” said Mark Merritt, the chief executive of the Pharmaceutical Care Management Association, which represents pharmacy-benefit managers and opposes the proposed federal rule.

But patient advocates say that the restriction of patients to mail-order programs has been particularly onerous for people with H.I.V. Often, they have close relationships with local pharmacists, some of whom specialize in treating people with the virus and are aware of the long list of additional medications that many patients must take.

Refilling medications through the mail breaks that bond, advocates say, and also increases the risk that patients will miss a dose if a refill is not delivered on time. Missing even a small number of doses can lead to a resurgence of the virus.

“We talk about everything that’s going on with you — it’s your whole life,” said Marva Brannum, the pharmacy manager and an H.I.V. specialist at Premier Pharmacy in the Los Angeles area. Ms. Brannum was mentioned in the lawsuit filed by Consumer Watchdog but she said she was not paid by the group. “In a perfect world, all of the physicians would be talking to one another and know what the other physicians are prescribing, but that doesn’t always happen.”

According to the lawsuit, Aetna’s new policy requires that all H.I.V. drugs be obtained through one of its divisions, Aetna Specialty Pharmacy. Early refills of the drugs are not permitted, so members have to call or fax each month to reorder their drugs.

In the statement, Aetna said that the 30-day limit on H.I.V. medications was not new, nor was the requirement that members refill their prescriptions each month limited to patients with H.I.V.

The limitation on supply, the company said, allows in-network pharmacies to check in more frequently with patients to help them cope with side effects or other problems. In addition, the company said, the pharmacists “check on a member’s drug and dose and help prevent waste if their dose changes. This helps save members money.”

But the lawsuit asserts that the new policy raises the out-of-pocket costs of the drugs. Previously, Aetna members had to pay $20 to $70 per prescription for H.I.V. drugs. Now they will be asked to pay 20 percent of the cost of the drug, up to $150, the lawsuit said.

Aetna said a patient’s out-of-pocket costs varied depending on the plan selected, and that payment assistance programs were available for some drugs.