You probably know that many companies are freezing or even eliminating their pension plans. Workers could once expect to collect a pension in retirement -- a "defined benefit" -- but today, many folks are being offered only "defined contribution" plans, such as 401(k)s, in which the amount that they (and sometimes their employer) contribute to the plan is set, but the eventual value of the account is uncertain.

Many big-name companies have frozen their pension plans. General Motors (NYSE:GM), the struggling carmaker; Sears Holdings (NASDAQ:SHLD), the hard-hit retailer; financial services giant Citigroup (NYSE:C); and Gannett (NYSE:GCI), the struggling newspaper and broadcasting company are some of the prominent names putting the brakes on defined benefits.

If you're patting yourself on the back for working for a healthy, growing company, don't think you're in the clear, though. IBM (NYSE:IBM), which sports net profit margins and recent revenue growth both exceeding 10%, froze its pension. So did Alcoa (NYSE:AA), whose stock has risen nearly 9% annually over the past decade. And don't forget Verizon (NYSE:VZ), among many other companies not exactly in their death throes.

The lesson here is simple: Don't assume your pension is safe. When companies freeze or shrink pension plans, they often benefit financially, so tweaking the pension program is an attractive option for many healthy companies. They can ditch the responsibility to cough up certain amounts of money for retirees, and they can more easily manage making set contributions to 401(k) plans.

There is some good news. If your pension plan goes belly-up when your company files for bankruptcy protection, you may still end up receiving some or all of your pension, thanks to the federal government's Pension Benefit Guaranty Corporation (PBGC). But the government won't make up for lost benefits if your company freezes or shrinks your pension.

So you should prepare yourself for the worst-case scenario of becoming pensionless. According to a 2007 report by Watson Wyatt, between 2001 and 2004, the number of Fortune 1000 companies that froze benefits increased considerably, from 5% to 11%.

The good news is that by planning and taking action now, you can still retire very well. Learn much more in our 401(k) guide and our IRA Center. And for detailed guidance on retirement planning, you can test-drive, for free, our Rule Your Retirement newsletter service. A free trial will give you full access to all past issues. Advisor Robert Brokamp regularly offers recommendations of promising stocks and mutual funds, too.

Longtime Fool contributor Selena Maranjian owns no shares of any companies mentioned in this article. Sears Holdings is a Motley Fool Inside Value recommendation. Try our investing newsletter services free for 30 days. The Motley Fool is Fools writing for Fools.