CBO said Friday that revenues grew one percent to about $2.5 trillion and expenditures increased by four percent to $2.9 trillion over the past nine months.
Surplus decreased from $50 billion in June 2015 to $10 billion last month, the agency noted.
According to CBO, the three-percent decline, or $12 billion, in revenue for the month of June 2016 is largely due to lower corporate income tax payments.
The agency also found that spending in the past month was $321 billion, up $28 billion from the prior-year period.
CBO said the Federal Communications Commission did not receive payments from auctions of electromagnetic spectrum licenses and the U.S. government spent $2 billion more on Medicare and Social Security programs last month.
The government also collected $2 billion less in payments from government-sponsored enterprises Fannie Mae and Freddie Mac while outlays for net interest on the public debt climbed by $5 billion, the report states.
These are the factors that CBO says triggered the overall spending increase during the month of June.