Transportation Secretary Sean Duffy said Thursday that air traffic controllers who don't show up for work during the shutdown won't get paid and could be let go from their positions.

"When you come to work, you get paid," Duffy said in remarks on Fox Business' Varney & Co. "We need the best and the brightest, the dedicated controllers, and if we have some on our staff that aren't dedicated, we're going to let them go."

Duffy claimed 53% of flight delays across the country are being caused by controller staffing shortages.

There are currently 1,613 delays nationwide and no FAA staffing triggers.

Some of the delays are due to other factors like runway closures or weather.

-ABC News' Clara McMichael and Ayesha Ali

The IRS said it will furlough nearly half of its workforce as "most IRS operations are closed" due to the lapse in funding.

According to the IRS contingency plan released Wednesday, out of 74,299 employees, 39,870 would be retained as exempt, while 34,429 would be furloughed.

The plan states that work related to protecting government property and revenue will continue, including processing tax returns with payments, maintaining online systems and operating taxpayer verification services. Most other operations like taxpayer assistance and audits would pause until funding is restored.

-ABC News' Will Steakin

The Senate on Wednesday held a sixth round of votes on dueling measures from Republicans and Democrats to fund the government. Both attempts to advance legislation failed, with the shutdown now stretching into its eighth day.

The Democratic-led government funding bill that includes health care provisions failed by a vote of 47-52. As was the case the previous five times the bill was voted on, no Republican supported it.

The GOP-led government funding bill that would reopen the government until Nov. 21 also failed to get the 60 votes needed, with the final tally being 54-45.

Employees at the IRS received an agency-wide email on Wednesday morning informing them that staff who are not "excepted or exempt" are being furloughed effective immediately due to the lapse in funding, according to an email obtained by ABC News and multiple sources.

The memo states that while all employees were receiving the notice, some staff are "excepted or exempt from the furlough based on their specific duties" and would receive separate instructions from their divisions. Unless employees were specifically notified otherwise, David Traynor, Acting IRS Human Capital Officer wrote, "you are being furloughed beginning October 8, 2025," and are instructed to cease work and enter non-pay, non-duty status.

The email to IRS staff also states that furloughed federal workers are legally entitled to receive full back pay once funding is restored, citing the Government Employee Fair Treatment Act of 2019. Trump has threatened not to give furloughed workers back pay, despite the law.

Multiple sources inside the IRS told ABC News the rollout of the furlough order has been "very chaotic," with some workers being left confused over whether they were exempted from the furlough, given they were told before the agency-wide notice and not afterward.

Sources told ABC News that some employees who had already left, assuming they were furloughed, were later called back, while others were told to "sit tight" as managers awaited clarification on who should keep working.

The Treasury Department and IRS did not respond to a request for comment. It's unclear exactly how many IRS staffers were furloughed but sources told ABC News multiple departments were impacted.

-ABC News' Will Steakin, Benjamin Siegel and Olivia Rubin

The Senate failed to advance the Republicans’ clean government funding bill that would extend government funding through Nov. 21 by a vote of 52-42. The government shutdown will continue into tomorrow.

The legislation would have needed 60 votes to advance.

Democratic Sens. Catherine Cortez Masto, John Fetterman and independent Angus King voted in favor of the bill. Republican Sen. Rand Paul voted against it.

No other senators flipped their vote. There were five absences: GOP Sens. John Curtis, John Kennedy and Thom Tillis, and Democratic Sens. Martin Heinrich and Jacky Rosen.

Aides have told ABC News that the Senate is expected to take the same two votes again tomorrow for a sixth time. There is at this stage no indication that the outcome will be different when the vote is called tomorrow.

-ABC News’ Allison Pecorin