In a rare move to block a major pharmaceutical deal, the U.S. Federal Trade Commission would sue to stop it amgen inc AMGN $28 billion acquisition of Horizon Therapeutics PLC HZNP.

Reuters reported that the FTC said Amgen could use its solid position to pressure insurance companies and pharmacy benefits managers into favorable terms on Horizon’s two key products — Tepezza, for the treatment of thyroid eye disease, and the gout drug Krystexxa.

Holly Vedova, director of the FTC Bureau of Competition, in Reuters reportcalled the lawsuit “the first recent FTC challenge to a pharmaceutical merger.”

“Rampant consolidation in the pharmaceutical industry has given powerful companies the ability to skyrocket prescription drug prices, deny patients access to cheaper generic drugs, and impede innovation in life-saving markets,” she added.

“Amgen is disappointed by the FTC’s decision and remains committed to completing this acquisition that will bring significant benefits to patients suffering from very serious rare diseases in the United States and around the world…” Amgen said in a statement.

“We have worked cooperatively over the past several months to answer the questions raised by investigative staff at the FTC and believe we have demonstrated overwhelmingly that this combination does not raise legitimate competitive issues,” Amgen added.

Seagen Inc SGEN Shares are also down 5.14% to $189.30 amid mounting fears the FTC could lockdown Pfizer Inc PFE Deal valued at $43 billion.

Merck & Co Inc MRK also agreed to the purchase Prometheus Biosciences Inc RXDX for around 11 billion US dollars.

Price promotion: HNZP shares are down 15.70% to $94.66 at last check on Tuesday and AMGN shares are down 1.91% to $229.04.