The estimated number of available jobs fell to 736,000 over the three months to May.
“Feedback from our vacancies survey suggests some firms may be holding back from recruiting new workers or replacing people when they move on,” said Ms McKeown.
The figures also showed that the unemployement rate rose from 4.5% to 4.6% – the highest in almost four years and could rise higher, according to Yael Selfin, chief economist at KPMG UK.
“It is likely that businesses will look to offset some of the rise in employment costs through a combination of reducing headcount and slowing hiring activity,” she said.
“Given this, we expect the unemployment rate to edge higher over the coming year.”
The rise in average wages slowed to 5.2% between February and April, easing from a 5.6% increase.
However, it remains above the rate of inflation, which increased to 3.5% for the year to April.
Chancellor Rachel Reeves announced the rise in National Insurance contributions by employers in last October’s Budget. The hike is forecast to raise £25bn in revenues by the end of the parliament.
Employment minister Alison McGovern said there were 500,000 more people in work since Labour won the election last July.
This is based on the number of people over the age of 16 in employment, which rose from 33.5 million between April and June last year to 34 million between February and April this year.
“People all over the country are benefiting from increased training opportunities,” said McGovern.
But Conservative shadow business secretary Andrew Griffith said the rise in the unemployment rate was “disappointing but no surprise”, adding: “Businesses are still absorbing a £25bn jobs tax.”
Liberal Democrat Treasury spokesperson Daisy Cooper said: “The chancellor’s pig’s ear of a jobs tax is crushing the growth potential of our high streets and small businesses.”
She added: “These figures could not be a clearer signal to the chancellor, ahead of the Spending Review, that the government must change course.”
On Wednesday, Reeves will announce the Spending Review, which will allocate funding for everyday public services such as the NHS, education and policing as well as investment in infrastructure.
The NHS and defence are expected to be among the main beneficiaries in the review, leaving other departments with squeezed budgets.
