An air carrier captain reported a disagreement with ZAU on altitude assignment.

Attributes
ACN	511000
Time
Date	200105
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	msl bound lower : 12000 msl bound upper : 13500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-300
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time type : 1654
ASRS Report	511000
Events
Anomaly	altitude deviation : undershoot other anomaly other
Resolutory Action	controller : issued advisory
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	Ambiguous

Narrative:

Ord departure control gave us clearance to climb FL230 with a turn heading 220 degrees. While climbing out of 12000 ft, ATC asked our altitude. After confirming passing 13500 ft on our way up to FL230, ATC informed us that the clearance was for a similar sounding call sign. I am sure he said air carrier xx for our clearance, which my first officer confirmed back to him when originally given.

Original NASA ASRS Text

Title: AN ACR CAPT RPTED A DISAGREEMENT WITH ZAU ON ALT ASSIGNMENT.

Narrative: ORD DEP CTL GAVE US CLRNC TO CLB FL230 WITH A TURN HDG 220 DEGS. WHILE CLBING OUT OF 12000 FT, ATC ASKED OUR ALT. AFTER CONFIRMING PASSING 13500 FT ON OUR WAY UP TO FL230, ATC INFORMED US THAT THE CLRNC WAS FOR A SIMILAR SOUNDING CALL SIGN. I AM SURE HE SAID ACR XX FOR OUR CLRNC, WHICH MY FO CONFIRMED BACK TO HIM WHEN ORIGINALLY GIVEN.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.