GEOFF BENNETT: As the government shutdown hits the one-week mark with no end in sight, President Trump today issued a new threat, saying that furloughed federal workers may not be reimbursed with back pay once the government reopens.

DONALD TRUMP, President of the United States: For the most part, we're going to take care of our people.

There are some people that really don't deserve to be taken care of, and we will take care of them in a different way, OK?

GEOFF BENNETT: That reverses what's been longstanding policy and possibly goes against a 2019 law that ensures back pay for federal workers.

Here with more on this is our White House correspondent, Liz Landers.

Liz, it has been a very busy day for you.

(LAUGHTER) LIZ LANDERS: Yes.

GEOFF BENNETT: So what exactly is the administration threatening to do here and why?

LIZ LANDERS: So "PBS News Hour" obtained this memo.

It's a draft memo that was written by the general counsel at the Office of Management and Budget.

And in it, they believe the administration has the interpretation of that 2019 law that they actually don't have to pay these furloughed federal workers any kind of back pay.

Now, that 2019 law was passed after the longest government shutdown in history to give protections to employees so that they would be assured to get back pay after that kind of shutdown.

GEOFF BENNETT: And it was President Trump who signed it.

LIZ LANDERS: And it was President Trump who signed it.

Excellent point.

In this interpretation from this new OMB legal counsel, they're basically saying that that 2019 amendment gives a permanent authorization for the furloughed workers to get back pay once the federal government reopens, but it does not require it.

There's also another sort of addendum in there that the administration is leaning into saying that the Congress, that, when they reopen the government, has to put this, the federal furloughed worker back pay, into whatever funding bill they're doing.

So they're trying to find some loopholes here.

And this was written for Russ Vought, who's the director of the Office of Management and Budget, and he has been working with the president, we know, to slim down the federal government threatening these mass layoffs through other kind of mechanisms.

So between this new memo and the mass layoff threats that we have been hearing, it seems like the administration is putting pressure on Democrats to end this shutdown.

GEOFF BENNETT: Quick question here, though, is this legal?

LIZ LANDERS: Well, according to a few people we talked to, probably not.

The largest federal workers union that I spoke with -- or that put out a statement earlier today said that this is an obvious misinterpretation of the law and also said that it is inconsistent with the Trump administration's own guidance from a few days ago, which said that furloughed employees should receive retroactive pay.

I also talked to Shalanda Young, who was Biden's OMB director, and she said that the 2019 law makes it very clear that Congress has the intent to pay these federal workers who've been furloughed.

She said that the federal government always pays federal employees once they have been furloughed.

And she also made the point that this will surely spur Congress to add this into the funding bill that they're working towards, but have not yet passed.