Auckland Mayor Len Brown is accusing the Government of jumping its own gun in trying to veto alternative funding such as road tolls for congestion-busting transport schemes.
He says it should wait until its officials complete a joint analysis with Auckland Council staff of the $2.86 billion underground railway proposal.
Mr Brown warned Local Government Minister David Carter that scrapping such projects from the regional transport strategy would have "a dire and unacceptable" consequence for congestion in the country's commercial capital.
Next in priority are $2.2 billion of upgrades through southeast Auckland, including a freight highway from Mt Wellington to Onehunga, and a third Waitemata Harbour crossing for more than $5 billion.
In a letter to the minister, Mr Brown has described as "entirely premature" a Government statement that it does not support assumptions in the new 30-year Auckland Plan about extra revenue sources to fill a transport funding gap of $10 billion to $15 billion.