An estimated 700 federal workers are paid not to do any work for the government and instead use all of their time doing activities on behalf of their union, allowed through a long-standing civil service practice called "official time."

The estimate is from a study by the Competitive Enterprise Institute, a libertarian think tank, and based on publicly available federal data and information obtained through the Freedom of Information Act. The study is titled "It Is Time To End Official Time."

"Activities performed on official time benefit only labor unions and their members, not the public. Furthermore, it is likely that thousands of federal employees spend 100 percent of their time performing union activity instead of the public service they were hired to do," said Trey Kovacs, CEI's labor policy expert.

Official time is defined by the Office of Personnel Management as "time spent by federal employees performing representational work for a bargaining unit in lieu of their regularly assigned work." In theory, official time makes it possible for federal employees who are shop stewards in their unions to take brief periods of time off for issues such as bargaining with management for new contracts. It was first allowed under the 1978 Civil Service Reform Act and is essentially viewed as a trade-off for certain limitations put on federal unions, such as prohibitions on striking.

However, a January report by the Government Accountability Office found that 346 Department of Veterans Affairs employees spent 100 percent of their time on official time. A 2016 report by the Social Security Administration identified another 15. FOIA requests by the conservative group Americans for Limited Government of 11 federal agencies found another 155 such workers. Those included: 26 at the Transportation Department; 29 at the Agriculture Department; 16 at the Environmental Protection Agency; two at the Small Business Administration; 17 at the General Services Administration; two at the Energy Department; three at the Education Department; 17 at the Labor Department; four at the Commerce Department, and 39 at the Department of Homeland Security. In 2013, then-Sen. Tom Coburn, R-Okla., identified 200 workers at the Internal Revenue Service who did nothing but official time.

Those are, the CEI report cautions, just the ones that have been identified. Figures are not available for several major agencies and departments. A 2014 OPM report, the most recent such report available, found that 3.4 million hours were spent on official time and put the cost to taxpayers at $162 million.

"Unfortunately, a general lack of transparency surrounding the practice makes it impossible to know what specific activities are performed on official time or what its costs are," Kovacs said.