Horizon Pharmaceuticals (NASDAQ:HZNP) dropped 1.9% on a report that Sen. Elizabeth Warren (D-MA) told the Federal Trade Commission she has concerns about Amgen’s (NASDAQ:AMGN) plan to buy Horizon Therapeutics (HZNP) and Indivior’s plan to buy Opiant Pharmaceuticals (NASDAQ:OPNT). Opiant fell 2.6%.

“Given these companies’ records of anti-competitive business practices, these acquisitions could cause further price increases on lifesaving drugs and prevent affordable alternatives from entering the market,” Warren wrote in the letter to FTC Chairwoman Lina Khan as well as other FTC commissioners, who are Democrats, according to a Reuters report.

Warren added that both Amgen (AMGN) and Horizon Therapeutics (HZN) “have engaged in brazen price increases,” according to the Reuters report.

Amgen agreed to buy Ireland-based biotech Horizon Therapeutics (HZNP) for nearly $27.8 billion in cash last month. Indivior (OTCPK:INVVY) agreed to acquire opioid overdose therapy maker Opiant (OPNT) for $145 million in November.

“The FTC should strongly consider Indivior’s history of anti-competitive and deceptive practices when evaluating how Indivior might behave after this potential transaction is completed,” Warren wrote in the letter, Reuters reported.

Warren is not new to being critical of M&A in the U.S. In recent months she has asked the FCC to block Tenga’s (TGNA) sale to Standard General deal as well and for the FTC to block Kroger’s (KR) planned purchase of Albertsons (ACI).

In March Warren and Rep. Mondaire Jones (D-NY) introduced legislation to block deals worth more than $5B or that lead to high market shares.