HMRC is reminding taxpayers that they have until Monday to ensure their paper self-assessment returns are filed.
Due to postal strike action, the Revenue advises people to send their returns as soon as possible to avoid late-submission penalties.
If a self-assessment is sent and misses the deadline, taxpayers will be liable to an automatic £100 penalty, which rises based on how late it's submitted past the deadline.
People won't usually need to send a return if their only income is from their wages or pension, or if they're newly self-employed, but their earnings don't exceed £1,000.
Almost half a million people choose to send their returns through the post rather than complete them online.
Anyone filing a paper self-assessment must visit the Government website, download the SA100 form, fill it out, and then send it to HMRC.
Those who submit their tax returns online have until 31 January to file their self-assessment and pay any outstanding tax.
Myrtle Lloyd, HMRC's director general for customer services, said:
"We understand some customers might be worrying about paying their self-assessment bill this year, and we want to support them. There is still time to set up a payment plan - to see if you're eligible go to GOV.UK and search ‘pay my self-assessment'."
Ask us about your tax returns.