Since November 1, 2010, at the request of the US government, all airlines operating flights to the United States are required to provide visa data for all passengers, as well as information about their place of residence in the US, no later than 24 hours before departure.

This information is required by the Transportation Security Administration (TSA) to identify known terrorists and prevent individuals on the No Fly List from boarding an aircraft.

Airlines are not permitted to board a passenger without special authorization from the US Transportation Security Administration. This means that if you do not provide the data on time, the airline has the full right to deny you boarding.

More detailed information on how TSA uses your data can be found on the US Transportation Security Administration website at the link: 
http://www.tsa.gov/stakeholders/secure-flight-program