(Reuters) - The U.S. Food and Drug Administration on Thursday listed a number of drugmakers it said could be improperly blocking access to their medicines in order to delay generic competition.

A view shows the U.S. Food and Drug Administration (FDA) headquarters in Silver Spring, Maryland August 14, 2012. REUTERS/Jason Reed/File Photo

But many of the companies immediately pushed back, saying the FDA list of drugmakers may be out of date and that some of the drugs included on it already have generic competitors.

The FDA said the list contained all of the inquiries about drugs it had received from generic drugmakers since 2005. It said companies generally do not inform it if they have made samples available after a generic developer has reached out to the agency.

Releasing the list of drugmakers, which includes Celgene Corp CELG.O, Johnson & Johnson JNJ.N, Gilead Sciences GILD.O and Novartis AG NOVN.S, is part of the Trump administration's efforts to pressure companies to lower drug prices.

Last week, U.S. President Donald Trump unveiled a “blueprint” aimed at doing that, but critics have said the proposals did not do nearly enough to substantially decrease the cost of drugs for consumers. Shares of drugmakers rose on Friday after Trump’s speech.

The agency said companies on the list may be using FDA safety regulations and other tactics to deny access to their medicines from generic drugmakers hoping to copy them.

Generic drugmakers may not be able to develop alternatives without access to samples of branded products they intend to copy, the FDA said.

“I want to be very clear: a path to securing samples of brand drugs for the purpose of generic drug development should always be available,” FDA Commissioner Scott Gottlieb said in a statement.

Gottlieb, who has made faster approvals of cheaper generic medicines a priority, said this should be true even in cases where there is limited access to drugs for safety reasons.

The FDA is notifying the Federal Trade Commission, which can investigate anti-competitive acts, of cases where drugmakers may be blocking access to their products if there is no safety reason, Gottlieb added.

The FDA said it had also heard of some drugmakers adopting tactics to make it hard for generic companies to purchase branded drugs even at a fair value in the open market.

Industry lobby group Pharmaceutical Research and Manufacturers of America (PhRMA) said it was concerned that the FDA list lacks context and conflates a number of issues.

“It is important to differentiate between those products for which FDA has received complaints as opposed to those products for which it has received a request for a safety determination letter,” PhRMA said.

Celgene, for example, argued that the three of its products on the FDA list all carry risk of significant side effects, including severe birth defects.

“These therapies are subjected to rigorous safety controls that have been developed by the company and approved by the FDA,” Celgene said in a statement. It noted that two of the three drugs already have generic versions licensed to enter the market in coming years, including multiple myeloma treatment Revlimid, by far the company’s biggest selling product.

A number of other companies said the drugs in question already had generic competition. Roche ROG.S, which was listed for acne drug Accutane, said it stopped making or selling the drug in the United States in 2009.

RBC Capital Markets analyst Brian Abrahams said in a research note that the effect of the FDA’s list will likely be limited.

“Though such efforts maintain the public concern about biopharma’s role in high drug prices and potentially anti-competitive practices, other than creating negative optics for these companies we see minimal impact such a list will have on actual generic risk,” he said.