IRS is the internal revenue service department of the US government. They collect taxes from the businesses and the people. Clearly their jobs will not be required under MLE. They can be dismantled. To avoid sudden chaos in the society, they can be slowly retrained to track the 40 hour plastic card system that the MLE will use. They will have to modify the software that IRS is using. They can become the human resource department of the government under the MLE. They will manage the hiring and firing of people and their relocation problems etc. They will define the jobs and they will find the need of the society under the MLE.
Similar methods can be implemented for many other corporations and departments of the government, which are meaningful now but will become unnecessary under the MLE. IRS is just an example of retraining of the people for the new life towards the MLE.