Opposition peers, who last week voted to stop Ken Livingstone standing for a third term as London Mayor, have attempted to backtrack.
Ken Livingstone has been elected twice as mayor
Liberal Democrat spokesman Baroness Hamwee and Baroness Hanham, for the Tories, said they had not meant the change to apply to next year's contest.
They want to set a two-term limit for any person holding the office.
But the peers have now said the rule should only apply after the London mayoral elections are held next year.
On Tuesday evening, Baroness Hamwee and Baroness Hanham suggested in a "tidying up" amendment to the Greater London Authority Bill that ministers should be able to delay implementation of the proposed limit until after May's poll.
Communities and Local Government Secretary Ruth Kelly has already pledged to ask MPs to overturn last week's government defeat when the Bill returns to the Commons.
Her junior minister, Baroness Andrews, dismissed Lady Hamwee's new amendment, which peers later rejected by 101 to 72, a government majority of 29.
Lady Hamwee told peers: "The limitation on the number of terms which a mayor might serve was not a personal attack on the current mayor.
"Nor do we feel that it is appropriate, so close to the May 2008 elections, to change the rules of the game."
Former Kensington and Chelsea Council leader Lady Hanham, who had led last week's Conservative move, said of the amendment: "This would clarify, I think, the position as to what we thought and believed we were approving."
Baroness Hanham warned last week the office had become "the nearest thing we have to a dictator".
Mr Livingstone was elected mayor in 2000 as an independent and re-elected in 2004 as the Labour candidate.