• Sen. Pat Toomey, R-Pa., said he wants to hear bankers defend stock buybacks and assure the GOP that political issues aren't influencing lending.
• "One of the things I'm hoping for, and I will urge these guys to do, is stand up and defend capitalism," he told "Squawk Box" on Wednesday morning.
• CEOs including JPMorgan's Jamie Dimon, Wells Fargo's Charles Scharf, Citi's Jane Fraser and Goldman Sachs' David Solomon begin two days of hearings on Capitol Hill later Wednesday.

The top Republican senator in charge of overseeing Wall Street regulation is hoping the chief executives of the nation's largest lenders will "defend capitalism" when they appear before his committee.

Sen. Pat Toomey, R-Pa., said that he wants to hear bankers defend the practice of stock buybacks and assure the GOP that political and social issues aren't influencing which businesses and individuals the lenders choose to underwrite.

"One of the things I'm hoping for, and I will urge these guys to do, is stand up and defend capitalism," he told CNBC's "Squawk Box" on Wednesday morning. "I hope they will defend the system that has created more opportunity and prosperity than any other system."

Banks need to "avoid the sort of appeasement of this whole movement that I see, in some cases, where I think political agendas are starting to creep into banking policy," he added.

Toomey's remarks came hours before Wall Street's top brass is scheduled to testify before Congress.

CEOs including JPMorgan Chase's Jamie Dimon, Wells Fargo's Charles Scharf, Citi's Jane Fraser and Goldman Sachs' David Solomon will kick off two days of hearings before the Senate Banking Committee, where Toomey is the ranking member.

The bank executives are likely to face gripes from both sides of the political aisle, with Democrats hoping to address racial differences in lending and Republicans keen to keep banks out of social and political commentary.

Toomey criticized what he sees as banks' bowing to social pressure and activist movements for curbing lending to certain industries, including fossil fuel producers and firearm manufacturers.

"The energy space is an interesting case. If these banks want to provide financing to relatively inefficient producers of energy, but they are green producers and therefore they want to provide subsidies for it, I think that's between the executives and their shareholders," he said.

"If they cross the line into saying, 'By the way, we will not make credit available to oil and gas development,' ... then you're making a judgment."

Democrats, led by Sen. Sherrod Brown of Ohio and Rep. Maxine Waters of California, are likely to grill the executives on their efforts to mitigate disparities in minority lending, as well as their support for small businesses.

Brown made clear from the start of his time as the head of the Senate Banking Committee that he wanted to hear from the nation's biggest banks more often. He said in January that he wasn't convinced that the Federal Reserve's regular assessments of the banks proved the group was in solid financial health.

"I'm not suggesting that CEOs of U.S. banks, of Wall Street banks, I'm not suggesting they're Deutsche Bank," the senator said at the time in a reference to investigations into the German bank.

"But I am suggesting that they have a lot of power and we need to know more about how they do their business," he added. "The more we hear from them, the better."

The two parties are all but certain to clash over banks' stock buybacks, a method of returning excess cash to shareholders that has come under fire from Democrats as a type of market manipulation used to inflate executives' pay.

Democrats say companies should use excess cash to raise worker wages and, when appropriate, return capital in the form of dividends.

Banks had been barred from share repurchases for much of 2020 as the Fed worked to assess the damage caused by the Covid-19 pandemic to financiers' balance sheets. The central bank reversed that position in December, when it said banks could resume buybacks in the first quarter of 2021.

Toomey, and fellow Republicans, have supported buybacks as a viable and reasonable way to return earnings back to a company's stakeholders.

"Let's be honest: A very substantial share of elected Democrats either openly consider themselves socialist, or they espouse socialist policies," the Pennsylvania senator said. "If you had a vote today on the Senate floor to ban stock buybacks, that might pass. That's how bad the situation is."