Caesars Entertainment Corp. and Education Management Corp. have been stymied in their efforts to influence Congress to change a Depression-era law that's designed to protect lenders, according to people with knowledge of the matter.

The casino company owned by Apollo Global Management LLC and the for-profit college backed by KKR & Co. tried last month to insert an amendment into an early version of the landmark U.S. transportation bill that would have rolled back part of a 1939 law known as the Trust Indenture Act, said the people, who asked not be identified discussing the actions because they haven't been made public. Without the changes, the companies may find it harder to win creditor lawsuits claiming actions they took to revise their debt violated parts of the act. 

Caesars has said it will probably have to join its bankrupt subsidiary in Chapter 11 if it loses the suits, which are over actions the company took to shuffle debt before the unit filed for court protection. Apollo, which controls Caesars along with TPG Capital, could then lose its stake entirely in the casino giant. Education Management may have to pay out junior creditors who didn't go along with its out-of-court debt reorganization, hurting the investment value of KKR, which is among the company's largest equity holders.