Treasury one-month bill rates turned negative for the first time since June as the government sells less of the short-term debt with seasonal tax payments flowing into federal coffers.

Rates on one-month Treasury bills touched negative 0.0051 percent for a second day, down from as high this quarter as 0.04 percent, according to Bloomberg data. The average rate for borrowing and lending Treasuries for one day in the repurchase market was 0.067 percent yesterday, according to the DTCC GCF Treasury Repo index, down from as high this month as 0.110 percent.

"Bill rates have started to decline as issuance has already been cut and will continue after the upcoming tax date passes, given more cash will be coming into the Treasury," Andrew Hollenhorst, fixed-income strategist at Citigroup in New York, said in a telephone interview. "There are less investable assets out there now for short-term investors."