Have You Ever Felt Sorry for the I.R.S.? Now Might Be the Time That may invalidate all the automatic withholding forms, or W-4s, that employees signed, Mr. Isberg said, “and put employers it the position of getting a new W-4 from every U. S. worker.” The burden of carrying out a new code also falls heavily on the I. R.S. Pete Isberg, vice president for government relations for ADP, one of the largest payroll providers, said taking account of the changes would be easier for the larger automated companies, but acknowledged that the short lead time between the law’s anticipated passage and the effective date would be a problem for some. Referring to enforcement, taxpayer services, and cybersecurity, Mr. Koskinen said, “We don’t have enough people to do all the work that needs to be done as a general matter,” let alone grapple with an overhaul of the tax code. R.S., in a statement on Thursday, said that taxpayers should not expect to see any changes as a result of the legislation to be reflected in their paychecks until February, and that the agency would work closely with payroll and tax professionals.