If you've already reached full retirement age, but you're not eligible to withdraw your application, you can choose to suspend benefits while you're earning income. This will allow you to earn delayed-retirement credits until age 70 for each month payments are suspended.
These hurdles shouldn't prevent retirees from returning to work if they need the income, as long as they take the potential pitfalls into account. For those still in the workforce dreaming of an early retirement, knowing how hard it can be to unretire might be the best argument for hanging in there as long as possible.
Alexis Leondis is a Bloomberg Opinion columnist covering personal finance. Previously, she oversaw tax coverage for Bloomberg News.