The Senate Finance Committee's hearing with executives from pharmacy benefit managers will hopefully soon be followed by legislation to bring drug prices down and end the "secrecy" in the drug industry, Chairman Sen. Chuck Grassley told CNBC on Tuesday.

Executives from CVS Health, Cigna, OptumRx, a subsidiary of UnitedHealthcare, Prime Therapeutics and Humana, are scheduled to testify later in the day about high prescription drug costs. PBMs, sometimes referred to as "middlemen," negotiate discounts with manufacturers for insurance plans and employers.

Grassley and other lawmakers suspect these so-called backdoor deals between drug companies and pharmacy middlemen contribute to the high drug costs some consumers see at the pharmacy counter.

"There's a lot of secrecy. There's not a whole lot of understanding of the role they play," Grassley said in a "Squawk Box" interview. "Our goal is to end this secrecy, get to transparency. With transparency comes accountability."

The hearing Tuesday, led by Grassley, and Sen. Ron Wyden, D-Ore., marks the committee's third on drug prices this year. In late February, the committee heard testimony from executives of AbbVie, AstraZeneca, Bristol-Myers Squibb, Johnson & Johnson, Merck, Pfizer and Sanofi.

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The pharma executives at the time pointed the blame at middlemen for pocketing discounts instead of passing them along to patients. The executives didn't commit to, or even suggest, lowering their list prices. Some referenced these prices as simply the price that's advertised, not what consumers actually pay.

High drug costs have become a rare bipartisan issue. President Donald Trump has made lowering prices one of the key issues of his administration, and Democrats are jockeying to prove they can lead reform.

Grassley said Tuesday there's already plenty of proposed legislation to bring down drug costs. He mentioned the CREATES Act, a bill introduced by Sen. Patrick Leahy, D-Vt., which aims to stop drugmakers from withholding samples of their medicines from generic manufacturers, thus increasing competition and lowering costs.