Changes in social security taxes were minimal under the new tax law. So this is a valid year to year comparison. Social security tax collected in June rose 2.2% vs. June 2017. The gain comes on the heels of a similar gain in May, and just a 1.7% gain in April. That means that Social Security tax collections have been consistently less than the rate of wage inflation, which ran 2.7% in each of the past 3 months.