Here’s one to make you pull out your calculator or your hair.

A growing number of retirees have stepped off the sidelines and headed back to work this year, but one thing that might surprise them is the impact that any income, even from part-time work, can have on their Social Security benefit.

I hear this all the time from retired family members, friends, and readers.

Roughly 1.5 million retirees have unretired and reentered the U.S. labor market over the past year, Nick Bunker, the director of economic research at Indeed Hiring Lab, told Yahoo Money.

“That’s more than 3% of retired workers who have made the decision to return to work, a continuation of a trend that started in the spring of last year,” he said.

The impetus for many has been soaring inflation and the volatility of the stock market rattling retirement accounts.

Unretiring is good news in my book. I’m a big fan of working as long as you can to build financial security to support a longer, healthier life span. And, of course, there are all the other good things that work in some fashion can provide like a social network, the psychological boost of feeling relevant and needed, and the mental engagement to use it before you lose it.

But the problem is some of those former retirees who were pushed out of the workforce due to a layoff or accepted early retirement packages in the first year or so of the pandemic decided to tap into their Social Security benefits for income. They were eligible if they were age 62 or older and figured it made sense to turn it on. I get that.

But that’s where things get tricky. The sweet new paychecks might trigger the Social Security retirement earnings test; a formula that withholds a portion of benefits if your wage income exceeds a set level.

“The Social Security earnings test is problematic even without the pandemic, but it's even more pronounced now,” Martha Shedden, president of the National Association of Registered Social Security Analysts (NARSSA), which has trained more than 3,000 advisors on how to help their clients make optimal Social Security decisions, told Yahoo Money. “There are quite a few people out there dealing with this because of what's happened in the past almost three years.”