Citigroup Inc. is winding down the first phase of a contactless payment test with the New York Metropolitan Transportation Authority.

In the New York City Transit Subway Trial, which began in 2006, Citi issues MasterCard Inc. contactless payment cards and fobs that people can use to pay their fare at some subway turnstiles.

In a letter sent Monday to trial participants, Citi said that the system will be switched off at the end of the month in preparation for the second phase of the test. In that phase, participants will be able to use contactless payment devices on other transit systems in the region, including some New York buses and New Jersey trains.

The letter did not say when the second phase would start, though Citi said last year that it would begin in the first half of this year.