In the past year, the combined pensions deficit of firms on the UK's FTSE 100 index has increased 13%, according to JLT Employee Benefits.
That could cause problems when some firms carry out pension re-valuations in the coming months, JLT said.
Tesco and Lloyds bank are among those re-valuing their pension schemes.
UK companies have to measure the deficit or surplus of their defined benefit pension schemes every three years.
"With many pension schemes now embarking on their triennial actuarial valuations and deficits likely to be much bigger than three years ago there are going to be some difficult discussions between companies and pension scheme trustees," said Charles Cowling, a director at JLT.
Companies could be forced to put much more money into their pension schemes to reduce the deficits, he said.
JLT found that the combined pension funds deficit of FTSE 100 companies was Â£60bn in April, up from Â£53bn a year ago.
The deficit of all UK private sector pension schemes was unchanged at Â£182bn, JLT found.
They "remain high due to quantitative easing and record low interest rates," Mr Cowling said.
Some of the UK's biggest companies face "difficult discussions" over their growing pension deficits, according to a pensions consultancy.