The letter warned of reports that House Republicans on the conference committee to the bill "will insist [that] controversial provisions from H.R. 7 be part of the final conference report even though H.R. 7 was never passed or even considered by the House of Representatives."

It also warned that several Illinois transportation groups also oppose the bill. While the House did pass a short-term extension that includes a requirement to approve the Keystone pipeline, the letter dismissed that bill, H.R. 4348, as a non-comprehensive measure that includes "unrelated policy provisions."

In contrast, the letter said the Senate-passed bill would keep several Illinois transportation initiatives alive. "While not perfect, the Senate-passed bill will maintain existing funding levels for Illinois transportation projects, improve Illinois's transportation network and save or create an estimated 67,900 jobs in our state."

Both Durbin and Costello are on the conference committee that will help negotiate a final agreement, and encouraged all members of the Illinois delegation to "share your priorities" for the bill.

"The conference committee is expected to hold a formal hearing when Congress reconvenes on May 8," they wrote. "The conferees are already beginning informal discussions about the contents of the final bill. It is incumbent upon us all to work together to ensure the final transportation bill reflects Illinois's unique place as the transportation hub of the United States."

Their letter was sent to Illinois's 11 House Republicans, seven House Democrats and Sen. Mark KirkMark Steven KirkHigh stakes as Trump heads to Hill Five things to watch for at Trump-Senate GOP meeting Giffords, Scalise highlight party differences on guns MORE, Durbin's Republican counterpart in the Senate.