Approximately 28% of senior business decision-makers in the UK are unaware that their minimum workplace pension contributions will increase on 6 April this year.
That is according to new research by NOW: Pensions, which finds that 42% are oblivious to a further rise next year, despite firms potentially being subject to fines if they fail to comply.
"Although these changes have been planned for a number of years, it seems that some employers still risk being caught out," NOW: Pensions director of policy, Adrian Boulding, said.
"The good news is, it's not too late to take action and there's plenty of support available for those that may be unsure what to do."
Minimum contributions into workplace pensions will increase from 2% to 5% of earnings next month, before rising again to 8% in April 2019 - potentially boosting employee savings by a third.
NOW: Pensions found that small businesses are most prepared, with four out of five aware of the upcoming changes this year, compared to 66% of large companies.
Among those that are ready for the changes, 92% also know that their business could be fined if they don't act.
This comes after research from the Association of Consulting Actuaries (ACA) found that 44% of employers do not want to increase their minimum contributions post-April 2019.
It was also found that the number of employees opting out of auto-enrolment is rising, and is expected to increase further over the next two years as mandatory minimum contributions rise.
The research forecasts opt-out rates to increase to 16-20% after April 2019, compared with the 11-15% at present, while these are already approaching 25% in smaller firms.
ACA chairman, Bob Scott, said: "The increases in contributions come very soon after their staging date for auto-enrolment, and land in the middle of pre-Brexit economic uncertainties.
"To give subsequent generations a decent chance of enjoying adequate retirement incomes, we call on the government to review its spending plans, tax rates and incentives."