The 2012 Smaller Firms' Pensions Survey looks at companies with fewer than 250 employees. The ACA found that payments into pension schemes have remained static since its previous report in 2010.
The combined contribution has been steady at 9% of earnings on average into trust-based schemes, and around 7% into contract-based plans.
ACA said the trend was "alarming" given longer life spans and the lower investment returns seen in recent years.
Businesses surveyed cited lower employer national insurance rates, less red tape and lower corporation tax as being on their wishlist to help them boost pension contributions, and encourage employees to pay more into pensions.