Firms will be asked to send their PAYE returns electronically from April this year through RTI-enabled payroll software every time they pay their workers.
This will replace an end-of-year return - a move HMRC hopes will lead to greater levels of accuracy and make it easier for employers to report information.
However, the department is urging any firm still unprepared for changes to get ready now.
Ruth Owen, HMRC's Director General Personal Tax, said that there is more to the changes than "simply buying or updating software".
"Employers may need to add employees such as casuals or those below the Lower Earnings Limit to their payroll system and must think about their payroll practices to make sure that they work for real-time reporting," she added.
The PAYE records of six million people are expected to be updated through RTI by the start of April.
Posted by Thomas Fletcher