Thousands of federal employees have been working without pay because of the government shutdown, which is now weeks long.

Eventually they will get paid. But they better hope that the back pay isn’t delivered to them as a lump sum.

Here’s what I mean. Let’s say a woman working for the Transportation Security Administration (TSA) — the folks who, among other things, tell you to take off your shoes at airport checkpoints — usually gets $2,000 a week. Without any other salary, that would probably put her in the 24 percent income tax bracket.

So around $480 would usually be withheld from her paycheck for income tax.

Now, let’s say the government shutdown lasts 10 weeks and she gets all the back pay — $20,000 (10 weeks X $2,000) — at once. If the payroll people at TSA don’t adjust, it will look to the computers like she makes $20,000 for a single week, or $1.04 million a year.

That would put her in the 37 percent tax bracket. And that means $7,400 will be taken out of that $20,000 check. If 10 weekly checks are issued at the 24 percent rate, then she’d pay just $4,800 in income taxes.

So, someone at the TSA’s union (and others that represent federal workers) had better make sure that doesn’t happen.