American Express (Amex) has halted projects starting November 22 citing “lack of clarity”, sources said, resulting in the loss of about six weeks of billing for vendors. TCS, Infosys, Cognizant Technology Solutions and Syntel are the major vendors for Amex. Infosys declined comment, so did TCS, citing the silent period ahead of results. Cognizant could not be reached. Amex did not respond to an email. Sources at one of the IT firms said some onsite employees had started returning to India, as work had reduced.