Last week, a government agency in Washington announced that it wanted to take over a retirement plan for pilots at United Airlines. This pension plan is supposed to hold nearly six thousand million dollars. But it has about half that, and United is in financial trouble.

Retired Americans get some money each month from Social Security. This is a federal program financed by employment taxes. But millions also depend on retirement plans offered by employers.

One such plan is called a four-oh-one-k, named after part of the tax law. Both the employee and the employer pay into the plan. The money they put in is not taxed. It is invested in stocks and other products. How much a retired worker gets depends on how much the investments return.

But a pension guarantees the amount that a person will receive. Pension plans are no longer very common.

Federal law requires employers to keep enough money in pensions to meet expected payments in the future. In the nineteen nineties, many companies did not need to pay into their pensions. A strong economy meant that pension-plan investments were enough. But since then, employers have had to make big payments. Some have found this difficult.

United Airlines says it can no longer pay into the pension for its pilots. The company also says it does not know if it can continue to pay into three pension plans for thousands of other employees. United is under bankruptcy protection from its creditors.

The Pension Benefit Guaranty Corporation is a government agency. It has insurance programs paid for by employers. It also earns money from investments. This agency takes control of pension plans that fail or are in danger of failing. Its job is to make sure workers receive their money.

Now the agency wants to block an agreement between United and its pilots union. That agreement would end the current pension plan. In return, the pilots would get an interest in the company once it leaves bankruptcy.

The Pension Benefit Guaranty Corporation says it is trying to protect United employees. The agency also wants to limit how much it might be responsible for if United cannot pay its pensions.

Creditors of the airline support the move. But the pilots union opposes it. The pilots could lose one hundred forty million dollars if a court approves an immediate takeover of their pension.