The Georgia NAACP is asking the U.S. Department of Justice to investigate what it says is the state's discriminatory practice of awarding transportation contracts.

The letter, from state NAACP president Edward DuBose to Attorney General Eric Holder, suggests the Georgia Department of Transportation has an "ongoing, systematic and deliberate practice of under-utilizing minority businesses."

The group's concern is based on a study commissioned by GDOT to examine its contracting practices. The report found that from 2009 to June 2011, the department used African-American owned firms in just 2.4 percent of its contracts while black-owned firms make up 14.1 percent of all companies available to perform construction and engineering work.

Sheila Jones, the state NAACP's community coordinator said Monday that the report "warrants our serious attention." Jones and others, including state Sen. Vincent Fort, D-Atlanta, said the report is another reason to vote against Tuesday's referendum to create a one-cent sales tax to fund transportation projects.

Transportation spokeswoman Jill Goldberg said the department has not heard from the NAACP regarding its Disadvantaged Business Enterprise program and said the civil rights group did not submit comments or attend five public comment meetings held since April on the disparity study.

"Therefore, it is impossible for us to respond to any purported particular criticism," Goldberg said. "The allegation that the GA DOT willfully discriminates against any segment of the population is irresponsible."