"It will have to happen over time because it will be costly."
The country's 43,345 public servants had a median base salary last year of $57,500.
The policy will give National further ammunition for painting Labour as the big-spending party.
Robertson's announcement was met by loud cheers at the first of 12 planned "hustings" meetings around the country. For the first time, Labour members and affiliated unions can vote for their party's leader, and the speeches and promises were carefully targeted at them.
Robertson's announcement gazumped rival David Cunliffe, who was expected to make similar announcements at the two meetings in Auckland today.
Cunliffe declared he, too, would repeal employment relations laws, and introduce a Government-wide living wage over time.
"It will be a strong package of policies that will put unions back in the centre of the fight for equality."
He denied it was simply an attempt to court the union vote, saying the party had always held a strong role in industrial relations.
"It has an industrial wing and a political wing. We will win when those two wings fly together."
Cunliffe said Labour had managed the economy well, while National was creating the first "deficit generation", in which the children would be worse off than their parents.
The third leadership contender, Shane Jones, focused on the need to build up small-town New Zealand.
He said he would focus more on Pasifika and working-class issues at today's South Auckland meeting and "more intellectual" issues for the audience in West Auckland.
After yesterday's Levin meeting, most members refused to say who they would vote for, at the urging of party president Moira Coatsworth.
However, one older man, Errol, said he believed Jones had won, without a doubt. "He spoke from the heart. I'd like to see him be the next prime minister."
Another, younger man said both Cunliffe's and Robertson's speeches were "particularly good".
"And I think Shane Jones' was exactly what you would expect - very witty and very clever."
