No sentencing date has been set for 36-year-old Pedro Palacios of San Antonio, who's free on bond.
Palacios on Monday appeared before a federal judge in Laredo and pleaded guilty to wire fraud.
Investigators say the man's father-in-law was treasurer of the Border Patrol Union Council Local 2455 at the time of last year's theft. Authorities say Palacios was hired by his father-in-law to repair a union computer and used the opportunity to steal the checks.
Palacios forged signatures on more than 60 checks and then deposited them electronically using cellphone software.