If you're holding a federal government check dated prior to Oct. 1, 1989 - and there are 5.5 million of you out there - you have one week to cash it. By next week, it won't be good anymore.

That doesn't mean you can't get another one, but you'll have to go to the government and ask for a replacement.Americans are sitting on between $2.5 billion and $3 billion in government checks more than a year old, according to Andy Montgomery, a spokesman for the Treasury Department's Financial Management Service.

A law that went into effect a year ago requires people with checks issued before last Oct. 1 to cash them not later than Sept. 30 - next Sunday.

The new law also requires people receiving checks written after last Oct. 1 to cash them within a year. All government checks now bear the reminder: VOID AFTER ONE YEAR.

After the deadline, the checks are automatically canceled. Until now, government checks were good indefinitely.

The deadline does not affect the government's liability, the Financial Management Service emphasizes. But once a check is canceled, a person must go to the federal agency that wrote it for a replacement.

Since the law went into effect, several thousand people already have brought in old checks, Montgomery added.