In 1986, Green won the Democratic nomination for the Senate against multimillionaire John Dyson, spending just $800,000 to Dyson's $6,000,000. Dyson remained on the ballot as the candidate of the Liberal Party. Green lost the general election to Republican incumbent Alfonse D'Amato who was supported by then mayor Ed Koch; Green filed a formal ethics complaint in the Senate Ethics Committee against D'Amato that resulted in the Senator being reprimanded by the United States Senate after media reports that suggested that nomination of D'Amato as a chair of the Senate Committee of Banking, Housing, and Urban Affairs had been tainted by illegal financing of his campaign to the Senate.