It could widen as Mr. Obama, seeking to harness anger over growing income inequality, escalates his criticism of the industry, after a year spent trying to smooth ties bruised by efforts to impose tougher regulations.

Since this spring, Mr. Romney has raised $1.5 million from employees of firms like Morgan Stanley; Highbridge Capital Management, a hedge fund; and Blackstone, a private equity firm. Mr. Obama has raised just over $270,000 from firms that were among his leading sources of campaign cash in 2008.

Employees of Goldman Sachs, who in the 2008 campaign gave Mr. Obama over $1 million — more than donors from any other private employer in the country — have given him about $45,000 this year. Mr. Romney has raised about $350,000 from the firm’s employees.