Campaigners have raised concerns over a ban imposed by HM Revenue and Customs (HMRC) on paying tax by credit card or via the Post Office.
About 11 million people complete a self-assessment tax return every year, with the deadline for online forms of 31 January approaching.
Payments at the Post Office were banned in December and the credit card option will be cut from 13 January.
Millions of people who have more than one source of income or are self-employed are required to file a tax return.
The tax due can still be paid by debit card, via a bank’s BACS, CHAPS or Faster Payments system, or by setting up a direct debit.
Employed people who owe less than £3,000 on their tax bill can pay it through their subsequent PAYE system, but only if they submitted their return online by 30 December.
However, the credit card payment option – used in 454,000 cases in 2016-17 – has been withdrawn owing to imminent change in the law which bans surcharges on Visa, Mastercard and American Express payments.