Businesses on the Employment Wage Subsidy Scheme (EWSS) could lose eligibility for the programme if they fail to provide Revenue with a six month sales projection before the end of the year.
It comes as Revenue published new eligibility criteria last Friday, following the enactment of the Finance Act 2020 last month.
Businesses will be required to compare financial projections for the period from January to June 2021, to actual reported turnover for the same period in 2019.
Revenue said that "reasonable, evidenced based assumptions" made to prepare the projections which form the basis of the eligibility review will be accepted.
Businesses must expect to experience a 30% reduction in turnover or customer orders between 1 January and 30 June 2021, compared with the actual reported turnover or customer orders during the same period in 2019 - in order to be eligible for the programme.
Following the changes, businesses will be also be required to review their eligibility at the end of each month, and carry out a self-review of its business circumstances.
If, based on this review, it is clear to the employer that they no longer meet the eligibility test for qualification for the scheme, Revenue said the employer must immediately cease claiming wage subsidy payments and de-register for the scheme.
It said subsidies correctly claimed in accordance with the terms and conditions of the scheme prior to deregistration will not be repayable.
Neil McDonnell, the chief executive of ISME, said the timing of the decision was less than ideal.
"Circulating that information on the Friday of the week before Christmas meant that many businesses and accountancy firms had already finished up for the holidays," he said.