(Reuters) – The U.S. Senate Finance Committee has invited executives from five pharmacy benefit managers to testify on April 3 on the rising costs of prescription medicines, in Congress’s latest effort to question industry officials directly over an issue voters consistently cite as a top concern.

Pharmacy benefit managers (PBMs) administer drug benefits for employers and health plans and also run large mail-order pharmacies. Drugmakers say they are under pressure to provide rebates to the handful of PBMs dominating the market to get their products included on preferred coverage lists.

PBMs have come under increased scrutiny both by President Donald Trump’s administration and lawmakers who say there needs to be more transparency about how drug prices get so high. The effect of rebates to PBMs are of particular concern.

The committee’s chairman, Republican Senator Chuck Grassley, and its top Democrat, Senator Ron Wyden, on Tuesday invited executives from UnitedHealth Group’s Optum, Cigna Corp, Humana Inc, CVS Health Corp, CVS Caremark and Prime Therapeutics LLC to the hearing, the third in a series examining rising prescription drug costs.

“There’s far too much bureaucracy and too little transparency getting in the way of affordable, quality health care,” Grassley and Wyden said, calling for the executives to provide real information and discuss real solutions.

The committee last month heard from seven pharmaceutical company executives. Its first hearing on Jan. 29 focused on insulin affordability.

(Reporting by Shradha Singh in Bengaluru and Yasmeen Abutaleb in Washington; Editing by Sonya Hepinstall)