The Illinois Supreme Court's May ruling finding the state's 2013 pension reform law unconstitutional will not be appealed to the U.S. Supreme Court, a spokeswoman for the state attorney general said on Wednesday.

"In the pension case, we asked the U.S. Supreme Court for a routine extension of time to allow us to consider whether to seek review of the case by that court," said spokeswoman Eileen Boyce. "After completing our analysis, we have decided not to ask the court to review the case."

In July, Illinois Attorney General Lisa Madigan was granted an extension until Sept. 10 to appeal the ruling, which rejected the state's argument that it needed to invoke police powers and cut pension benefits to deal with a fiscal emergency.

The unanimous ruling by the Illinois justices was based on a provision in the state constitution that prohibits the impairment or diminishment of public worker retirement benefits.

That provision was also used by a Cook County Circuit Court judge in July to void a 2014 pension law aimed at shoring up the shaky finances of two Chicago retirement systems. The state supreme court is expected to hear Chicago's appeal in November. (Reporting By Karen Pierog; Editing by Alan Crosby)