"No match" letters had been sent for years, but there was no penalty for failing to clear up the situation. Mostly, employers ignored the letters. Sanctions are now threatened, so the new "no match" letters are potentially of considerable importance as an immigration enforcement measure. Unfortunately, there will be literally millions of U.S. citizens also affected by the "no match" letters and some percentage of those affected will be contacting the Social Security Administration.
No one has any idea what effect the new "no match" letters will have upon the Social Security Administration's workloads. This may be little more than a blip or it may be a tidal wave. The Social Security Administration has been quiet about the potential workload problems that may arise from this. I cannot help thinking that Michael Astrue has been afraid of saying anything, since the "no match" letters are a major part of the President's plan to deal with illegal immigration and illegal immigration is a major issue for Republicans, in particular. The sheer unpredictability of the situation would scare me if I were Michael Astrue.