Greens Senator Bob Brown says Government electoral reform legislation to be debated in the Senate on Monday will mean tens of thousands of voters, disproportionately young and black, will miss out on voting.

The Electoral and Referendum Amendment Bill (No. 2) 1998 dramatically shortens the period before an election when people can enrol or re-enol to vote.

"This provision will mean young people and those who generally move house more are much more likely to miss-out on voting at the next election," said Greens Senator Bob Brown.