The Deputy First Minister has declined to echo Tory leader Ruth Davidson's pledge not to raise income tax in Scotland higher than the rates and bands in the rest of the UK when new powers are devolved to Holyrood.
Scotland will gain complete control over income tax rates and bands as part of the devolution package in the new Scotland Bill.
Ms Davidson said investors, businesses and families will seek assurances that devolved taxes will not mean higher taxes and urged her political opponents to make a similar pledge to give an early assurance to Scottish taxpayers.
The SNP's John Swinney, who is the Deputy First Minister and Finance Secretary, was questioned in a BBC interview about the Conservative leader's pledge not to raise income tax above UK rates.
"You would not echo that?" he was asked.
Mr Swinney told the Sunday Politics Scotland show: "I can't give that pledge today and I won't give it.
"Because I want to make sure that my party has the opportunity to exercise the choice that we believe to be appropriate in the relevant circumstances, the 2016 election and beyond, to ensure that we take the right decisions."
Asked whether he would have any intention of increasing or reducing both rates of income tax, Mr Swinney said: "We'll obviously give consideration to that as we formulate our proposals for the 2016 election and for subsequent budgets beyond that if we're fortunate enough to be the government of Scotland."
Mr Swinney pointed to changes already made by the Scottish Government to a property sales tax.
The Land and Building Transaction Tax (LBTT) replaced stamp duty on April 1 this year.
"What we've demonstrated already, with the tax powers that have been deployed to us on stamp duty and on landfill tax, is that at the first available opportunity the Scottish Government has acted on those taxes," Mr Swinney said.
"On stamp duty, we've changed it very radically to reflect our principle position that we believe tax should be structured on the basis of ability to pay."
Questioned on whether he was "implying" that he would seek to vary income tax in some respect, Mr Swinney replied: "I've implied nothing. I'm simply telling you that we'll exercise those responsibilities when it comes to formulating our manifesto for the 2016 election."
Responding to the interview, Scottish Labour said the SNP had "again failed to back" a 50p rate for those earning over £150,000 a year to pay for public services.
The party's finance spokeswoman, Jackie Baillie, said: "The SNP seem determined to shed policies from their manifesto as quickly as possible. Just a few weeks ago they were boasting about making Labour bolder, now they have gone quiet on fair taxes to invest in our most important resource - our young people.
"The problems in Scottish education are mounting up. Overworked, exhausted teachers, a Higher exams fiasco, literacy and numeracy rates falling and an attainment gap which shows Scotland a divided country when it comes to opportunities for young people.
"Whilst the SNP sit on their hands, Scottish Labour has a plan. We would ask those who earn the most to pay a little more tax to invest in the schools and kids with the least."
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