Labour’s Rachel Reeves ruled out increases to income tax or national insurance on Sunday if the party wins the general election.
The shadow chancellor made the pledge after saying both she and Labour leader Sir Keir Starmer want taxes on working people to be lower, although she noted she would not put forward "unfunded proposals".
Speaking to BBC One's Sunday With Laura Kuenssberg programme, Ms Reeves also said she did not want to make any cuts to public spending but was unable to give cast-iron guarantees and instead pointed to the need to conduct a spending review if she was in the Treasury.
She later declined to put a timeline on when a Labour government would increase defence spending to 2.5% of gross domestic product (GDP), a measure of the size of the economy.
Ms Reeves also said there is "not going to be a return to austerity" under Labour with commitments to boost frontline services a "down payment on the changes that we want to make".
She said: "But in the end we have to grow the economy, we have to turn around this dire economic performance."
Labour and the Tories traded insults about the other on Sunday as each claimed the other was shunning the doorstep.
The Conservatives suggested Sir Keir lacked the "stamina" to campaign after he was not seen publicly on Sunday.
Meanwhile, Labour said the Prime Minister had been "holed up with his aides" and "hiding away in his mansion" after he returned to his Yorkshire constituency to meet local veterans on Saturday following a two-day tour of the UK.
The parties had earlier clashed on the economy, with defence also set to be a live topic of debate.
During her broadcast round on behalf of Labour, Ms Reeves said she would not put a “timetable” on Labour’s plans to increase defence spending to 2.5 per cent of GDP.
The Conservatives have also pledged 2.5% in defence spending.
"We've committed to do in government a strategic defence review to make sure that we're getting value for money for all of our spending, including on defence where some of the procurement costs of purchasing new equipment have, frankly, got out of control under this Government,” said Ms Reeves.
It comes as Rishi Sunak announced plans to make eighteen-year-olds carry out a form of national service if the Tories win the July 4 poll.
Young people would be given a choice between a full-time placement in the armed forces for 12 months or spending one weekend a month for a year “volunteering” in their community, the Tories said.
The announcement came despite a defence minister ruling out national service in comments made just a day after the election was announced.
Opposition critics have dismissed the plans as unserious, with Labour saying the pledge would never come to fruition and amounted to “another unfunded commitment”.
