Washington (AFP) - Concerns over flight delays and missed paychecks due to the US government shutdown escalated Wednesday, as senators rejected yet another bid to end the standoff.

Democrats voted for a sixth time to block a Republican stopgap funding measure to reopen government departments, keeping much of the federal workforce home or working without pay.

With the shutdown in its eighth day, lines at airports were expected to grow amid increased absenteeism among security and safety staff at some of the country’s busiest hubs.

Air traffic controllers – seen as “essential” public servants – are kept at work during government shutdowns, but higher numbers are calling in sick rather than toiling without pay, leading to shortages.

Staffing problems have already been reported in almost a dozen airports from Chicago and Boston to Burbank and Houston, according to the Federal Aviation Administration (FAA), with further issues expected at Newark, a major hub for the New York City area.

Transportation Secretary Sean Duffy told CNN on Wednesday that he was “encouraging air traffic controllers to show up for work,” after noting an increase in use of sick days earlier this week.

“We’re having maybe a bit of rebellion by air traffic controllers caused by the shutdown,” Duffy said. “The problem is, when I’ve talked to them, they are stressed out. They are wondering, how do they put food on the table?”

Duffy said little more than half – 53 percent – of current delays are a result of lack of staffing, as compared to about 5 percent in recent months, before the shutdown.

“My message to them: they work for me. They got to go to work, show up, control the airspace, and eventually they get paid,” Duffy said.

- No end in sight -

Aviation monitor FlightAware reported around 10,000 flights delayed on Monday and Tuesday.

Although this is not thought to be an unusually high number, the FAA warned it could worsen.

“As Secretary Duffy said, there have been increased staffing shortages across the system,” it said in a statement.

“When that happens, the FAA slows traffic into some airports to ensure safe operations.”

There appears to be little hope of a quick end to the shutdown, with Democrats refusing to back any funding bill that doesn’t offer an extension of expiring health care subsidies for 24 million people.

Senate Majority Leader John Thune has been forcing votes most days on a temporary fix passed by the Republican-led House of Representatives, each one failing to garner sufficient Democratic votes.

Meanwhile Trump continues to wield the threat of turning many of the 750,000 enforced absences – known as furloughs – into permanent layoffs.

A draft memo circulated by the White House this week said furloughed workers aren’t guaranteed compensation for their time off – meaning many could lose out on back pay.

Some federal workers – including US Capitol Police – are set to miss part of their pay for the first time on Friday – amping up pressure for Congress to end the crisis.

A bigger so-called pain point comes next Wednesday, when 1.3 million active-duty service members – as well as tens of thousands of National Guard members and thousands of Coast Guard personnel – are due to miss their first paycheck.