Following a lengthy report by Pro Publica, U.S. Rep. Rashida Tlaib joined calls for an investigation into whether contributions by billionaire Dan Gilbert contributed to Opportunity Zone tax breaks for some of his largest developments in downtown Detroit.

Opportunity Zones are meant to provide tax breaks for developers working in “distressed communities.” Those areas are outlined in census tracts designated by the U.S. Treasury Department—the ones in Detroit are some of the wealthiest in the city.

Quicken Loans, the Gilbert-owned mortgage lending company headquartered in Detroit, donated $750,000 to President Donald Trump’s inaugural fund. Gilbert has invested billions of dollars in downtown real estate and gotten hundreds of millions of dollars in tax breaks, though the exact amount received through the Opportunity Zone legislation isn’t known.

Last week, Tlaib sent letters to the chairs of the House Ways and Means committee and two subcommittee urging an investigation into the program. “This is yet another example of how corporate greed and the influence of billionaires have infected our government like a disease,” Tlaib wrote.

On October 31, Sen. Cory Booker, Rep. Emanuel Cleaver, and Rep. Ron Kind also signed a letter urging Congress to look into possible political influence.

Jared Fleisher, Quicken Loans vice president of government affairs, penned a rebuttal piece in the Detroit News.

Every major planning document and strategy identifies these areas—the west riverfront, Corktown and the western portion of downtown—as economic development focus areas and targets for investment. It would be unthinkable— malpractice even—to not include this area in an economic development program, which is why the city included it.

The Rock Family of Companies has also since set up a website that responds to the charges in the Pro Publica article.

It’s not clear if or when Congress might investigate.