HARRISBURG, Pa. — Republican U.S. Sen. Pat Toomey and his Democratic challenger Katie McGinty tangled Monday over the use of corn ethanol in motor fuel and post-recession bank regulations as they try to show that the other favors big corporations over regular people.

Anti-Wall Street and anti-corporate themes have coursed through TV ads in Pennsylvania’s neck-and-neck Senate race, while both Toomey and McGinty have tried to position themselves as a fighter for the middle class.

Democrats have labeled Toomey as a “millionaire” former investment banker who defends tax subsidies for oil exploration companies and advances Wall Street’s agenda in the Senate.

In turn, a new Toomey campaign TV ad says the freshman senator “fights against corporate welfare … big bank bailouts and giant corporate handouts” while saying McGinty “gamed the corporate welfare system to line her own pockets.”

On Monday, Toomey highlighted the financial struggles at a Philadelphia-area oil refinery, Philadelphia Energy Solutions, and the role played by ethanol blending costs.

The use of corn ethanol is an economic harm to Pennsylvania, provides no environmental benefit and is “another example of how Katie McGinty loves to pick these corporate welfare programs that enrich a handful of huge agribusiness companies at the cost of average families and consumers and workers,” Toomey told reporters on a conference call.

McGinty, a long-time clean-energy advocate who served as a top environmental policy adviser to former Gov. Ed Rendell and former President Bill Clinton, supports the use of corn ethanol as a renewable fuel that can replace the need for some fossil fuels, according to her campaign.

A 2007 federal law requires companies to blend billions of gallons of ethanol into their gasoline. But it has come under scrutiny as to whether it reduces pollution and the Environmental Protection Agency is expected to produce a report on the impacts of biofuels by December 2017.

Toomey has co-sponsored legislation that would kill the fuel-blending requirement that is typically satisfied by corn ethanol, but leave intact a separate requirement for refiners to blend in different renewable additives, albeit at smaller amounts.

Meanwhile, McGinty took issue with Toomey’s efforts in Congress to change the oversight of the 5-year-old Consumer Financial Protection Bureau, a federal office created to protect consumers in financial dealings with banks, lenders and credit card companies.

The agency is in the news after it levied its highest-ever fine on San Francisco-based Wells Fargo last week. The bank said it will pay a $100 million fine over allegations its employees illegally opened millions of unauthorized accounts for their customers in order to meet aggressive sales goals.

“We’re here to call on Pat Toomey to change his tune and for once stand with consumers instead of just with the big banks,” McGinty said in a conference call with reporters. “This is yet another instance where his loyalties remain with his colleagues and partners and employers in the big banks instead of his own constituents.”

Toomey should use his position on the Senate banking and finance committees to investigate Wells Fargo’s practices, she said.

Asked about the bureau, Toomey said fraud can be prosecuted without inventing the agency, and he criticized its leadership structure as unusually unaccountable for such a powerful federal agency.