Auto-enrolment began in October 2012 and is rolling out from the largest to the smallest employers across the UK. All employers, including charities and the public sector, will eventually need to assess their workforce and automatically enrol eligible workers into a pension scheme.
The National Association of Pension Funds (NAPF) welcomed the news, but said the "real test" is yet to come.
"We are pleased that auto-enrolment has got off to such a great start and that there is strong support for saving through workplace pensions," said NAPF chief executive Joanne Segars.
"However, the real test will come when small and medium-sized employers, who have fewer resources and less pensions know-how, start enrolling staff next year.
"The challenge now is for the Government and The Pensions Regulator to make sure these employers understand what they have to do to comply."
The Pensions Regulator said this month's auto-enrolment registration report showed that more than 3,500 employers have now joined the scheme.
Pensions minister Steve Webb said: "Over 3,500 employers so far are helping us to create a fairer society by ensuring that pensions are no longer the preserve of the few. And the message to employers is: make sure you're ready for the date your workforce joins those already in."
