The Trump administration released a proposed regulation on Monday to force drugmakers to put the list prices of their products in TV ads, setting up a showdown with the pharmaceutical lobby.

“Patients deserve to know what a given drug will cost when being told about the risk or benefits it may have,” Health and Human Services Secretary Alex Azar said at the National Academy of Medicine annual meeting.

The regulation was previously announced in the Trump administration’s May blueprint for combating high drug prices. It applies to drugs that are covered under Medicare and Medicaid.

The proposed regulation, which will be finalized after a public comment period, said that the list price to be included must reflect the cost of a 30-day supply of the product.

[Related: Trump triggers fight over drugs with proposal to require price disclosures in ads]

The pharmaceutical lobby has fought back on the regulation.

The Pharmaceutical Research and Manufacturers of America, the drug industry’s top lobbying group, said on Monday that all of its 33 members agreed to develop a website that includes the list price and average out-of-pocket costs of their products. The drug companies would feature a link to the ad in their TV advertising for products but not for digital or radio.

PhRMA argues that putting in just the list prices in ads would be confusing to consumers because prices do not include context, such as rebates or discounts.

But the group was not specific on key aspects of their voluntary program, including how the companies calculate the advertised out-of-pocket average cost.

Azar bashed the industry initiative as a way to distract from the new regulation.

“We appreciate their effort, but placing information on a website is not the same as placing it in an ad,” he said.

It remains unclear if PhRMA will challenge the regulation in court. The group declined to speculate during a call with reporters Monday.

An administration official said that the regulation only targets TV advertising because that is the biggest share of direct-to-consumer advertising by drug companies. The administration added that it believes that by applying the regulation only to drugs covered under Medicare and Medicaid then it will cover "virually all drugs," even though the government programs don't cover some products.