Illinois senators don’t want the pending merger between American Airlines and US Airways to affect plans to expand O’Hare International Airport.

Last night, Senators Dick Durbin (D) and Mark Kirk (R) sent American Airlines a letter saying they hope the merger won’t derail the O’Hare expansion plan.

The billion dollar O’Hare Modernization Program hinges on agreement United and American Airlines. The city is scheduled to sit back down with the two carriers in March to work on the next phase of the decade-long project.

In 2011, Transportation Sec. Ray LaHood helped broker a deal between the federal government, the city and the airlines.

In the letter, the Senators reminded the airline the O’Hare project “will create 195,000 more jobs and generate $18 billion in annual economic activity,” adding the merger faces “regulatory scrutiny” by legislators before being approved.

Speaking today from Chicago, Sen. Durbin said the project was crucial.

“We really believe that key to economic progress in the Chicago reason is new runways and the modernization of O’Hare,” Durbin said. “I’d like a committment from the new American Airlines that they are going to with us in that effort.”

Staff from Senator Durbin’s office said they had not yet received a response from American.

“We appreciate the concerns expressed in the letter by Senators Durbin and Kirk,” American spokeswoman Mary Frances Fagan said, adding, “We have frankly been a little bit busy of late.”

Fagan reiterated what the airline said yesterday during its merger announcement, that Chicago remains an important hub, but declined further comment.

Here’s the full letter sent yesterday:

Durbin Kirk Letter to AA and US Airways - Merger - 2.14.13 by