One of the main things that the middle class did to try to fight back against the threat of big business was to push for the reforms of the Progressive Era.
In the decades before the Progressive Era, big businesses had been getting more and more powerful both economically and politically. This was eroding the power of the middle class. In the Progressive Era, the middle class fought back. It pushed for political reforms such as the direct election of senators and initiatives and referendums that would lessen big businesses' ability to "buy" government officials and government policies. The middle class also pushed for economic reforms such as antitrust legislation and laws that would protect workers.
By pushing for economic and political reforms in the Progressive Era, the middle class was fighting back against big business.