The man got out of his van and walked over to the lorry after being held up during rounds on the Tan y Bryn Estate in Valley.
When the driver rolled down his window the man spat in his face before leaving, officials said.
They called the attack "disgusting and cowardly".
Biffa, who have held the contract for collecting waste on Anglesey since 2004, said the incident was a "new low" for the company.
Regional manager Andrew Dutton said: "This was an unprovoked attack on a member of staff who was out doing his job for the community."
Meirion Edwards of Anglesey council said the incident was cowardly.
"We realise that sometimes people get annoyed if they're held up by recycling lorries, but all we ask for is a little patience," he said.
"Unfortunately, this incident wasn't captured on CCTV - but members of the public should be aware that most of the Biffa wagons are now fitted with cameras.
"As a council, we won't tolerate any aggressive or violent behaviour toward our contractor's staff, and will fully support Biffa with any future prosecutions."
A driver spat in the face of a bin man after getting stuck behind a lorry during recycling collections on Anglesey, council officials said.