While the federal government prepares to furlough workers in critical agencies starting next month, it's spending millions of dollars on employees who are "absent without leave" or simply showing up to work on "standby." 

In other words, complains one senator, workers "being paid to do nothing." 

Sen. Tom Coburn, R-Okla., is now urging the government to crack down on this alleged waste, saying targeting these workers could yield billions of dollars in savings -- and even avert some furloughs. 

"It makes little sense to furlough air traffic controllers and border patrol agents while retaining employees who are AWOL, on standby, not performing official duties, or sitting idle awaiting security clearances," Coburn wrote in a letter Wednesday to John Berry, director of the Office of Personnel Management. 

His complaints about workers being paid for "nothing" fall into several categories. 

In one are employees paid to work on "standby" -- those told to stay at their station during "longer than ordinary periods of duty" whether or not they're actually working. 

Coburn says a Congressional Research Service memo prepared for his office found at least 999 employees got "standby pay" in 2010, as did 906 in 2011 -- at a two-year cost of $13.1 million. 

Then there's the issue of AWOL workers. Coburn pointed to a 2008 report released by his office that found between 2001 and 2007, nearly 20 million AWOL hours were logged across 18 departments and agencies. This covers time when employees were late or otherwise absent without permission. 

In addition, Coburn said many workers are being paid for time spent performing unofficial duties -- like union-related activities. Plus the senator wrote that government contractors are occasionally "being paid to do nothing." He cited the example of contractors "sitting idle" while they await a security clearance. 

Coburn, in his letter, asked for details on the amount of money spent in these areas in more recent years. 

"As a starting point, agencies can avoid furloughing or laying off those performing the key functions of the agency by first eliminating to the greatest extent possible those who are not showing up for work, who are not performing official work, or are simply not working at all," Coburn wrote. 

An OPM official said the agency is currently reviewing the letter and "will respond as appropriate."  

The agency has not said whether these areas are being examined for further cost savings. 

Meanwhile, federal furloughs are poised to go into effect starting next month, while some agencies are still trying to delay or find ways around them. 

The Defense Department last week decided to delay issuing furlough notices to potentially hundreds of thousands of civilian workers, while it examines the issue. 

The Federal Aviation Administration is expected to furlough many of its 47,000 workers due to the sequester.