In many cases, that notice can simply be ignored, but you have not provided enough information for us to know. If the sponsor is the US Citizen Petitioner, and their job will continue once in the USA, just ignore it. If the liquid assets of the petitioner and applicant combined are well over three times the income requirement, ignore it. This is a stock message anytime the "total income" number on the latest tax return is below the 125% of the poverty line.
Please clarify the source(s) and amounts of whatever it is the Petitioner is using to qualify?