Mr Fiveash warned that the “continuous pressure” on employers could push businesses to reduce pension contributions at a time when Britain already faces a big retirement savings shortfall.
He said: “We’ve got a significant savings gap already and we are heading towards a crisis for people that think they’re saving enough and they’re not.”
Just one in seven workers is making large enough pension contributions to be able to maintain their living standards into retirement, according to analysis by Phoenix, Britain’s largest long-term savings firm.
Workers in the existing auto-enrolment system make minimum pension contributions worth 8pc of their salaries. This consists of a 5pc contribution by the employee and a minimum contribution of 3pc by their employer.
Businesses that give employees contributions larger than 3pc, which are typically in more highly paid sectors, may now opt to cut back as a way to absorb the blow from the NICs rise, while others could forgo planned increases, Mr Fiveash warned.
The pensions industry has long been pushing for the minimum 8pc threshold to be increased to 12pc, but reform will now be even harder, he added.
Mr Fiveash said: “We were hoping what the Government would announce was going to set a timetable for increasing minimum contributions. I expect that now might be delayed because of this. That’s the most disappointing thing.
“We need to get to 12pc and the longer we delay that, the worse that situation becomes.”
On top of the NICs increase, businesses will have to pay for a 6.7pc increase in the National Living Wage announced by Ms Reeves, as well as the costs for Labour’s Employment Rights Bill, which the Government’s impact assessment said will be as much as £4.5bn.
A government spokesman said: “With our public services crumbling and an inherited £22bn fiscal black hole from the previous government, we had to make difficult choices to fix the foundations of the country and restore desperately needed economic stability to allow businesses to thrive.
“Through our landmark pensions review, we are exploring options to expand on the success of automatic enrolment while boosting investment and increasing pension pots.”