Welsh Secretary Peter Hain has insisted the UK Government will push through a change to Welsh assembly election rules despite a defeat in the House of Lords.
Mr Hain says candidates currently have an "each-way" bet
Peers voted by a majority of 19 on Wednesday to continue the current system where candidates can stand in both constituency and regional lists.
Mr Hain said on Thursday that the existing system was an "abuse".
He added that the Lords' decision would be reversed when the Government of Wales Bill returns to the Commons.
The government's defeat came as peers began detailed consideration of the Bill, which will give new powers to the assembly government.
Liberal Democrat and Conservative peers backed a Tory amendment allowing dual candidacy to continue.
The lords voted for the amendment by 133 votes to 114.
Labour has said its an abuse of democracy for candidates who lose in constituencies to get into the assembly by also standing on their party's regional list.
Currently, 20 of the assembly's 60 members are elected from regional lists, with 40 elected by constituency vote.
Mr Hain told BBC Radio Wales on Thursday that Labour remained committed to ending the practice of candidates saying to do so was a manifesto commitment.
He said: "There is widespread abuse where candidates are elected on lists - often the majority of them having lost in the constituencies which they also stood for.
"So the voters rejected them in those constituencies, but they end up winning on lists.
"I think it's an abuse - if you're defeated and end up winning and setting up in the very same constituency where the voters kicked you out that is an abuse.
"We had a manifesto commitment to implement this ban on duel candidature - to put the voters in charge rather than the parties or the candidates having an each-way bet.
"Defeated candidates set up constituency offices as regional list members and try to undermine the elected member."
Mr Hain criticised the Lords for voting on amendments to a bill which had formed part of Labour's 2005 general election manifesto.
He said: "If the House of Lords persists on 'ping ponging' on this issue it may will risk getting royal assent for this [Government of Wales] bill by the summer.
Twenty assembly members are election via regional lists
"That will put in jeopardy the whole process of change we need to get in place before the May elections next year.
"Should the unelected Lords be able to overturn the elected government's policy decision?"
Responding to Labour plans to continue with election reform, Liberal Democrat MP Lembit Opik said: "There's no consistency in the Labour position - up in Scotland there's at least one Labour minister who stood on the dual mandate of a list and also tried to get in a seat.
"The pretence that this is all about making the Welsh system more democratic simply doesn't stand up."
Plaid Cymru parliamentary leader Elfyn Llwyd said: "On current voting trends, there's nothing in it for Labour on the lists anyway - this is purely a party-political gerrymandering exercise."
Conservative AM for Mid and West Wales Glyn Davies said the House of Lords had seen that "Labour is trying to force through an utterly reprehensible constitutional change which stinks of hypocrisy and election rigging".