Security concerns could bring Metra Electric, South Shore, Amtrak and Canadian National trains to a halt When the summit is held May 20-21.
Metra executive director Alex Clifford says he expects to know more by the end of the month.
The rail line is making contingency plans.
Commuters may have to quickly change their plans as well.
"None of that is comfortable for us but we're working with a very difficult situation," Clifford said. "And we have to appreciate what the secret service has to do. And we're pushing on them to let us know as soon as possible."
Clifford says that as soon as Metra gets the word from the secret service they'll pass it along.