Northern Ireland employers are being urged to get ready for major Pay As You Earn (PAYE) changes that come into effect in three months' time.
From April employers must PAYE returns electronically, using RTI-enabled payroll software, to HMRC each time they pay their employees as part of routine payroll processes.
The returns will include details of pay, tax and deductions.
This new process will replace sending a separate return at the end of the year.
Ruth Owen, HMRC's director general personal tax, said: "It's vital employers act now, if they have not already done so.
"Employers will need to send their first return - called a 'Full Payment Submission' or 'FPS' for salary or wage payments made to employees on or after April 6 - and if they have 250 or more employees they will have to send an Employer Alignment Submission before the first FPS."
She added: "There is more to it than simply buying or updating software - although this is key. 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."