The total number of employers fined for failing to comply with their workplace pensions duties reached 169 by the end of 2014, according the Pensions Regulators quarterly report.
The vast majority - 166 - were issued in the last quarter of 2014. Prior to this period, just three were issued since the regime came into force in July 2012.
According to the report Automatic enrolment compliance & enforcement, between October and December 2014 there were 1,139 compliance notices issued to employers instructing them to remedy a breach of their duties or risk a fine or further action from the regulator.
Each employer has a different "staging date" when automatic enrolment comes into force, depending on the size of the firm. The deadline for an employer to declare their compliance is five calendar months from their staging date.
Charles Counsell, director of automatic enrolment at the Pensions Regulator, said: "The vast majority of employers complete their duties on or ahead of time, but we are seeing a small minority that require the additional nudge of a notice from the Pensions Regulator."
Counsell said: "It appears some medium[sized] employers waited for a prompt from the regulator before completing their automatic enrolment duties. Employers must complete all their duties, including making their declaration of compliance to the Pensions Regulator."
Nathan Long, head of corporate pension research at Hargreaves Lansdown, said: "The message from the Pensions Regulator is loud and clear. Not complying is not an option. The crackdown is crucial to the continued success of auto-enrolment."
Long said that employers "should sit up and take notice". He added: "The Pensions Regulator is prepared to use the stick as well as the carrot to ensure compliance."