Shares in Pfizer (NYSE:PFE), Merck (NYSE:MRK) and Amgen (NSDQ:AMGN) fell slightly this morning after President Donald Trump tweeted that he was working on a “new system” to lower drug prices.

“I am working on a new system where there will be competition in the Drug Industry,” he wrote. “Pricing for the American people will come way down!”

PFE and MRK shares were trading down 1.1% this morning, while AMGN shares dropped 1.4%.

This is not the new administration’s 1st attack on the industry’s drug pricing strategies. In January, he said that pharmaceutical companies were “getting away with murder” with what they charge the government for drugs.

“We’re the largest buyer of drugs in the world, and yet we don’t bid properly,” he said at his 1st press conference. “We’re going to start bidding, and we’re going to save billions of dollars over a period of time.”

In his 1st address to Congress, Trump said more should be done to bring down “artificially high” drug prices and called for speeding up drug approvals within the FDA.

A January meeting with executives from pharmaceutical companies including Johnson & Johnson (NYSE:JNJ), Amgen, Merck and Eli Lilly (NYSE:LLY) seemed to signal a defusing of tensions.

During the meeting, Amgen CEO Robert Bradway reportedly committed to adding 1,600 U.S. jobs at his biotech.

Eli Lilly and Merck told Reuters that they were encouraged by the President’s focus on innovation and that the meeting also touched upon issues like negotiating stronger trade agreements, tax reform and getting rid of outdated regulations.

Yesterday, a group of senators requested pricing information from Marathon Pharmaceuticals for its $89,000 muscular dystrophy drug.

“The circumstances surrounding the development of Emflaza, and the benefits that will accrue to Marathon as a result of its approval of the drug, raise serious questions about whether there is any justification for such a dramatically high price,” the senators wrote.

Material from Reuters was used in this report.