Labour has warned that the economic downturn caused by coronavirus must not "increase the gap" in income and wealth between the north and south of England.
In a speech, deputy leader Angela Rayner urged the government to think of the "human cost" of unemployment.
She also argued that the stamp-duty holiday would help people in London more than those anywhere else.
Boris Johnson has promised to "level up" the country, helping parts feeling "left behind, neglected, unloved".
Last month, the prime minister set out a ??5bn plan to build homes and infrastructure as part of measures to deal with the expected massive recession following the nationwide lockdown.
The UK economy shrank by 2.2% during the first three months of this year, according to official figures - the joint-largest quarterly fall since 1979.
And the Office for National Statistics' data for April show a monthly fall of 20.4% - by far the biggest on record.
In a pre-recorded speech for the Durham Miners' Gala, the annual labour movement and trade union celebration which takes place online on Saturday, Ms Rayner spoke of her fears that the government might use the downturn to justify a policy of "managed decline" for northern England.
She said: "The north-south divide is continuing to grow and we cannot afford for the economic impact of coronavirus to increase this gap even more.
"The Tories talk a good game on this issue but their record of turning their backs on the North speaks for itself."
In his summer statement this week, Chancellor Rishi Sunak announced a temporary holiday on stamp duty on the first ??500,000 of all property sales in England to reinvigorate the property market.
Ms Rayner, citing research by the Resolution Foundation think tank, said this would not help the average homebuyer in north-east England, while the average buyer in London would save ??14,200.
She added that the large rises in unemployment seen in former industrial areas of the North during the 1980s should not be allowed to happen again.
Labour is keen to regain many former safe seats across northern England and the Midlands - once known as the "red wall" - that it lost in December's landslide general election victory for Boris Johnson.
Last month, the prime minister said his plans would ensure "jobs, jobs, jobs" and that there would be no return to austerity during the coronavirus downturn.