The IRS lowered the withholding tables in 2018 which required employers to then withhold at lower rates. This was done because of the Tax Cuts and Jobs Act of 2017 which lowered several income tax rate brackets. See more information below:
https://ttlc.intuit.com/replies/3301788
Also, you can adjust your withholding for 2019 by utilizing TurboTax’s W-4 Withholding Calculator
