The Department for Work and Pensions said that firms with fewer than 50 employees will get more than a year extra to comply with the new rules, which oblige them sign up staff for pensions unless they opt out.
They had been due to start from Spring 2014. The deadline has been moved until after the next election in 2015.
"Making staff in small businesses wait even longer before they get the right to an employer contribution to their pension is a grave disappointment", said TUC General Secretary Brendan Barber
The National Association of Pension Funds had warned that putting off the scheme would be highly damaging. Workers in small businesses are the least likely to be covered by existing pension arrangements.
Firms will eventually have to contribute at least 3% on top of each employee's salary and the employee at least 4%. Tax relief would take the total contribution to a minimum of 8% of pay.
The biggest companies will have to meet the auto-enrolment rules from October next year, as before.
"We recognise that small businesses are operating in tough economic times so we are softening the timetable for implementation to give them some additional breathing space," said the Pensions Minister, Steve Webb,.
He added that all businesses remain "in scope" to be covered by the new rules.