Soon after his inauguration, in 1902 Roosevelt persuaded Congress to create a new cabinet department, the Department of Commerce and Labor. This department included a Bureau of Corporations.
The task of the Bureau of Corporations was to gather information about companies in order to determine if they were acting in the public interest. The Bureau had the power to inspect the books of all companies doing business across state lines (interstate commerce).
In the cartoon below, scanned from Puck April 20, 1904, the view is that investigations by the federal goverment will "let the air out" of the trusts. Ideas about curbing business practices through investigation and publicity went well back into the 19th century.
This inspection power, along with the administration's revival of antitrust prosecutions under the Sherman Act, proved very important, especially after the Supreme Court struck down the Northern Securities Company for violating the Sherman Act.