Chief executives of the UK's largest companies will receive official notification of their auto-enrolment responsibilities from The Pensions Regulator this week.
A letter from TPR chief executive Bill Galvin is the first phase of the massive education and compliance campaign run by the regulator, as part of its enforcement role.
A five point check list and auto-enrolment information factsheet are also being sent out.
The introduction of auto-enrolment and compulsory employer pension contributions is being staged across the UK from next year. The largest employers will take on their duties from October 2012, through to the final companies by September 2016.
Companies with more than 120,000 staff will be the first to receive the information this week.
The regulator said in the next six months, nearly 600 of the largest organisations employing about a third of the UK workforce (around ten million employees) will have received letters marking 18 months to their particular duty date.
In due course, every employer in the UK will have received at least two letters as they approach their duty date.
MGM Advantage pensions technical manager Andrew Tully said: "While the introduction of auto-enrolment still seems a long way off, it makes sense to begin working out the impact the changes will have on your scheme.
"Financial plans are often made three years ahead, and auto-enrolment will be starting to impact on many employers by then.
"The TPR guides are a good basis to help work out what needs to be done, and how to communicate any changes to employees."
In the letter, Galvin (pictured)said: "The law requires you to automatically enrol certain of your workers into a pension scheme. The date by which you need to act is based on the size of your largest PAYE scheme and is likely to be 1 October 2012. The exact date by which you need to act will depend on the number of persons in your largest PAYE scheme on 1 April 2012."
He added: "Preparing for the changes in the law will involve your pensions, finance, HR and IT departments. It will be necessary to provide your whole workforce with information about how they are affected by these changes.
"We will soon publish detailed guidance on our website about the new employer duties and how to comply with them. The guides include information on identifying what duties apply for each person that works for you, the process of automatic enrolment, and the changes you may need to make to your existing pension arrangements."
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