The business secretary has said Labour’s manifesto pledge not to raise national insurance applied to employees but he did not rule out raising employers’ contributions in the budget.

Speaking on Sky’s Sunday Morning with Trevor Phillips, Jonathan Reynolds was asked if the pledge applied to employees’ and employers’ national insurance contributions (NICs).

He replied: “That pledge, it was taxes on working people, so it was specifically in the manifesto, a reference to employees and to income tax.”

He said he would not say anything more before the budget, but his comments have fuelled speculation that a rise in employer contributions is being considered. “There’s a lot already in the manifesto, but you have to wait for the detail of a budget,” he said.

NICs are paid by employees and employers and it has been unclear whether Labour’s promise not to increase the tax included both.

During prime minister’s questions on Wednesday, Keir Starmer declined to rule out raising employers’ NICs in the budget.

The shadow work and pensions secretary, Mel Stride, said it would be an “absurdity” for Labour to argue that raising employers’ NICs was not a breach of its manifesto commitments.

Stride said Labour had “boxed themselves in” by claiming it was not going to have to put up taxes, “and therefore saying that they would not put up all sorts of different taxes, broadly based taxes that account for about 75% of all the taxes raised”.

He said: “That leaves you with a narrow field of taxes now to go for. I think if they go for employers’ national insurance, firstly, it’s a very bad tax to raise, because it’s a tax on jobs, and what they should be about is growth and increasing productivity in the economy.

“The second thing is, I think it goes totally counter to their manifesto that assured us they would not be putting up national insurance.”

Stride also said the government’s claim that the Conservatives left a £22bn hole in public finances was “fictitious”.

The chancellor, Rachel Reeves, has said the Labour government inherited a £22bn “black hole” from its predecessors, causing speculation about how she will raise funds.

The Institute for Fiscal Studies (IFS) estimated this week that £25bn would need to be raised in tax increases if Reeves wanted to keep spending rising with national income.

The chancellor has also hinted she is planning to tweak the rules that dictate how much the government is allowed to borrow for spending on infrastructure investment. Writing in the Sunday Times, Reeves said it was “time that the Treasury moved on from just counting the costs of investments, to recognising the benefits too”.

Charlie Nunn, the chief executive of Lloyds Bank, told the BBC on Sunday that he was concerned about the impact of taxing employers’ pension contributions.

He said: “Anything that helps people continue to invest and take appropriate risk, we think, is really important. Anything that does the opposite would be a handbrake.

“Pensions, and contributions to pensions, are critical. We see about 40% of people in the UK have a pension which won’t give them even a basic living allowance when they retire. So we need to increase enrolment and investments in pensions.”