The government shutdown has already had a huge impact on the U.S., with hundreds of thousands of federal employees on furlough and millions more affected by the secondary consequences of the disruption to related businesses. Yet among all the things the government isn't doing during the shutdown, one stands out as having a huge potential impact on just about every member of the American public.

The Labor Department announced last week that it would not release September's report on the Consumer Price Index. Given how unimportant inflation has been over the past several years, the absence of a CPI report might not seem like a big deal. Yet the CPI is more than just an important gauge of price behavior. It also helps determine several key measures that affect millions of Americans. Let's take a look at how the shutdown's delay of September CPI data could affect you.

Social Security increase
Every year, Social Security recipients get an increase in benefits based on the change in the Consumer Price Index. Although the increase takes effect on Jan. 1, the months that the Social Security Administration uses to measure the cost of living adjustment happen to be July, August, and September. As a result, the CPI report originally due for release tomorrow would have been the last link in determining the COLA for 2014.

When you take the average level of the CPI-W for the three relevant months in 2012 and compare it to the levels for the two available months this year, you get a raise of between 1.4% and 1.5%. Until the actual figures come out, though, it's unclear how Social Security will deal with the uncertainty. As a result, recipients will have to wait for confirmation of their final COLAs.

Inflation-adjusted bonds
Another area where the CPI comes into play is in determining values of Treasury Inflation-Protected Securities. The bonds that exchange-traded funds iShares Barclays TIPS Bond (NYSEMKT:TIP) and iShares Barclays 0-5 Year TIPS (NYSEMKT:STIP) invest in have their principal values determined by changes in the monthly CPI. Currently, the Treasury Department has daily figures calculated through the end of October, but beyond that it would need September's CPI figure to do accurate projections.

Technically, the number would only be critical for maturing securities, and with no TIPS scheduled to mature until January, Treasury has time before the issue becomes problematic. But for the many investors who buy and sell TIPS, not having certainty about inflation calls into question one of the key reasons for owning the securities in the first place. Moreover, rates for Series I Savings Bonds are also set using September's CPI figure; with those new rates set to take effect Nov. 1, a lack of a CPI figure in time would disrupt that market as well.

Union contracts
Companies often negotiate labor deals with workers that refer to the CPI as a baseline for wage changes. Without a CPI against which to calculate those increases, workers won't be sure how much more they'll get paid.

Admittedly, fewer employees have automatic pay escalation in their contracts than in the past. During the financial crisis, the United Auto Workers made concessions to Ford (NYSE:F) that resulted in the elimination of cost-of-living increases for many workers. For decades, General Motors (NYSE:GM) tied wages to increases in the general cost of living as well as productivity gains, but GM's bankruptcy resulted in substantial renegotiation of union contracts to reflect the company's poor economic condition.

Yet for many government workers, CPI-linked cost-of-living adjustments will make a material difference to pay. Until CPI is determined, though, those workers can't be certain of their fate.

Stay tuned for more on the CPI
The Consumer Price Index might seem like a relatively unimportant number, especially with inflation largely under control right now. But the CPI actually affects many parts of the U.S. economy, and until things get back to normal, you'll have to deal with the uncertainty involved in not having precise inflation data.

Tune in to Fool.com for Dan's regular columns on retirement, investing, and personal finance. You can follow him on Twitter @DanCaplinger.

Fool contributor Dan Caplinger has no position in any stocks mentioned. The Motley Fool recommends Ford and General Motors. The Motley Fool owns shares of Ford. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.