Amazon has pledged to expand its same-day service to underserved people in the 27 cities in which it currently operates, and not to launch the service anywhere else without being able to cover every zip code, according to a letter obtained by Bloomberg reports. The move follows a Bloomberg investigation in April that found the company's same-day delivery service was biased in favor of white customers in some regions; for example, the report found that black residents in Atlanta, Chicago, Dallas, and Washington were "about half as likely" to be eligible for same-day delivery as white residents.

Amazon is working to expand its delivery footprint, which will rectify the disparity in cities that are not fully covered. "Very shortly, we will be expanding Prime Same Day service to every zip code of the 27 cities where Prime Same Day delivery is currently launched," the company said in a statement given to Bloomberg by the Congressional Black Caucus. "We will further not launch the service in any new regions, until we are able to secure a carrier for every zip code." Amazon says it is "still figuring out the details," but that complete coverage should be achieved "shortly."

Additionally, The Verge obtained a letter from Amazon sent to Representative Bobby Rush (D-IL), in response to an inquiry he made regarding Bloomberg's original report. In the letter, dated April 29th, Amazon VP Brian Huseman stated that the company is "actively working to enable service to Southside Chicago," and explained the method behind how it selects same-day delivery markets. Those factors include how far away fulfillment centers are, the number of Prime members in an area, the company's estimation of customer demand, and whether its partners can deliver goods until 9PM every day. A person familiar with the matter tells The Verge that Amazon is expanding its delivery capabilities and that it is working to fill gaps in its existing markets.

In April, Amazon denied that demographics had anything to do with where it decides to deploy the delivery service, claiming that it starts by focusing on ZIP codes that have a lot of Prime members. Amazon VP Craig Berman told Bloomberg that "demographics play no role in it. Zero." Nonetheless, the strategy had clear demographic consequences.

Update May 8th, 8:26PM ET: This story has been updated to include a letter sent to Representative Bobby Rush. Additionally, it now contains information from a source familiar with Amazon's same day delivery operation.