Brooksby previously told the AP that he had never failed a drug test or taken "bad substances".
The ITIA said that Brooksby accepted the first and third missed tests but disputed the second one.
Brooksby has 21 days to appeal against the decision to the Court of Arbitration for Sport (CAS).
"The whereabouts programme is a vital tool in maintaining a clean sport," ITIA CEO Karen Moorhouse said in a statement.
Reporting by Amy Tennery in New York; editing by Clare FallonOur Standards: The Thomson Reuters Trust Principles.
Persons:
Jenson Brooksby, Norway's Casper Ruud, Carl Recine, Brooksby, Karen Moorhouse, Amy Tennery, Clare Fallon
Organizations:
Melbourne, Tennis Integrity Agency, AP, Sport, Thomson
Locations:
Melbourne, Australia, New York