Chancellor Rachel Reeves defended the employer tax increase in last week's Budget, while saying she was “not immune” to the criticism it received.
However, she said funds needed to be raised to put public finances back on “solid footing”.
The decision to increase national insurance contributions paid by businesses has been criticized by many businesses, including GPs, who say it could harm services for patients.
New Conservative Party leader Kemi Badenoch criticized the move, telling the BBC it would not lead to growth and would “make us all poorer”.
From next April, employers will have to pay NI at 15% on salaries above £5,000, instead of 13.8% on salaries above £9,100 currently.
The Institute of General Practice Management, which represents GP practice managers, estimated the increase would increase the average GP practice's tax bill by around £20,000 a year.
Appearing with the Laura Kuenssberg show on Sunday, Reeves was asked if there was any chance she would rethink increasing national insurance for employers.
“I am not immune to their criticism,” she said, “but we must raise the necessary funds to consolidate our public finances.”
Reeves said the program to increase Employer NI was not on the party's agenda ahead of the general election.
Asked if she was wrong to say during the election that there would be no extra taxes if Labor won, she replied: “What I was wrong about, it was the mess the previous government left us,” citing the £22 billion black budget. hole that Labor says the Conservative Party has left them.
Earlier in an interview with Sky News, Reeves said “I was wrong on June 11, I didn't know everything” when she said during the election campaign that a tax rise would not be necessary.
Speaking to Laura Kuenssberg, Badenoch said Reeves' plan was “not coherent.”
She did not say whether she would cancel the increase in employers' NI, but said she would cancel the VAT rise on private schools, calling it “an aspiration tax that will make no money”.
