You may have read information regarding the Social Security maximum taxable wage base reported to be $128,700 for 2018. The Social Security Administration announced, on November 27, that the amount was changed to $128,400. You might want to check with your payroll peeps to make sure they are aware of this change.
Also, the IRS released 2018 Withholding Tax Tables on January 11. Employers should start using them ASAP, but no later than 2/15/18. The IRS is still working on updating the W-4. Continue to use the W-4 on file for calculating employee withholding. For more information see Notice 1036 https://www.irs.gov/pub/irs-prior/n1036--2018.pdf