Scottish Liberal Democrat leader Nicol Stephen has urged the Scottish Government to work with his party to scrap council tax.
Mr Stephen said it was time to team up with the Scottish National Party to bring in a local income tax.
He was speaking at the Scottish Lib Dems spring conference, the first since the party lost power in May last year.
Mr Stephen also outlined his vision for more powers for Holyrood and hit out at the Nationalists' record in power.
During his speech on Saturday afternoon he announced a series of groups to look at issues from energy needs to constitutional matters.
The Lib Dems and SNP both want a local income tax, but have disagreed on some of the detail on how to go forward.
Throwing down a challenge to First Minister Alex Salmond, Mr Stephen told delegates in Aviemore: "If you are serious about a local income tax, work with us.
"Bring together now, in good faith, those in Scotland who want to see the council tax scrapped and replaced by a local income tax."
He added: "When you find that the poorest pensioners pay six times as much of their income in council tax as the richest people, you know that something has gone very wrong with fairness in Scotland."
However, if a deal could be struck, the two parties' votes in the Scottish Parliament would still fall short of the majority needed to make the policy a reality.
The former Scottish deputy first minister, whose party served in coalition with Labour for the first eight years of devolution, also attacked "obscene" power companies whose profits rose along with the costs of electricity.
The National Grid, Mr Stephen claimed, had failed to understand the needs of renewable energy.
He went on to give his backing to plans for an offshore supergrid and announced a new energy commission, advised by Richard Yemm, who created the Pelamis wave energy generation scheme in Scotland.
Mr Stephen told the Lib Dem party faithful: "Isn't irony rich when the National Grid, the very organisation that should be creating the new supergrid, that gets fined £42m this week, not for cutting corners to do things fast, but for deliberately blocking new technology, like smart meters that can reduce energy costs in every household - that is obscene.
"It is obscene that when power prices go up six times the rate of inflation, power companies' profits go up 500%. The companies that should be making the big profits are Scotland's renewable energy companies."
Mr Stephen went on to place a high priority on the Holyrood-sanctioned commission on Scotland's constitutional future, announcing that the Steel Commission, headed by Lib Dem veteran Sir David Steel, would be reformed to create pressure for change.
Amid concern over detention without trial, DNA retention and ID cards, the Scottish Lib Dem leader also announced his own "stop and search hit squad" to keep an eye on any laws brought forward by the UK Government which would "erode civil liberties".
Mr Stephen said another new group would look at ways of encouraging young people to get involved with communities and politics.
Nicol Stephen preparing his conference speech
And he said the Lib Dems' had set a goal of doubling the number of poorest children going into further education, while finding ways to strengthen vocational skills.
Turning to his political rivals, Mr Stephen hit out at the pro-union Conservatives, claiming they had sided with the Nationalists, adding: "The Scottish Tories got hitched to the SNP and walked away from their promises before the election."
And he said of his former government partners: "As the main challengers in Scotland the last time, we can deliver a crushing blow to Labour next time.
"At Holyrood, they are simply unable to comprehend the position they are in - shell-shocked and shattered. No ideas and no impact."
'The Sun King'
Mr Stephen wondered if the SNP, since coming to power at Holyrood, had become "a little too full of themselves".
He told delegates: "Did you know they have tabled not one but two motions in not one but two parliaments, entitled 'god bless the SNP government'."
Mr Stephen asked: "And what of the Sun King? The first minister?
"He has surrounded himself with adoration and is blessed with a dutiful array of courtiers.
"They constantly commission opinion polls that have all the scientific rigour of Hans Christian Anderson."