Federal employees facing internal probes and other disciplinary action have been permitted to remain on paid leave for months on end -- sometimes for periods of over a year -- and now lawmakers on Capitol Hill want to know why.

The alleged abuse of administrative leave policy has been most egregious at the Department of Veterans Affairs where two of the officials whose actions touched off the VA scandal last year have been on paid leave for the last 18 months. They're not alone -- of the nearly 6,000 VA employees put on administrative leave between 2011 and 2013, 46 individuals have been paid not to work for more than a year.

Senate Judiciary Committee Chairman Chuck Grassley, R-Iowa, is pressing for answers.

"Every agency uses this leave differently, some agencies use it too extensively, and the taxpayers get short-changed," he said in a statement to FoxNews.com.

Part of the problem is a lack of legal guidance on what's actually allowed. Grassley blamed a "statutory and regulatory vacuum on the right use of paid leave."

But for Grassley and others, the way it's being used at the VA and other agencies clearly doesn't pass the smell test.

In fiscal 2014, the VA outspent all other agencies surveyed with respect to employees on administrative leave for a month or more. And Grassley says the agency has not provided congressional investigators with a full accounting of the reasons why.

In an Oct. 23 letter to VA Secretary Bob McDonald, Grassley complained its explanations were "incomplete and confusing" and cited one example of an employee who had logged over a year of administrative leave though his absence was technically authorized as three days of "New Employee Orientation."

The VA did not respond to calls for comment from FoxNews.com.

Grassley also sought answers from the Department of Homeland Security by Nov. 2 to questions about 88 agency employees getting paychecks while on leave for a year or more. According to his office, four were on leave for three years or more.

A committee spokesman told FoxNews.com the DHS provided a less-than-complete accounting.

In justifying the length of the leave, DHS said many individuals could not be reassigned because of the seriousness of the allegations against them -- and there was insufficient evidence to actually terminate them.

According to a source close to the committee, Grassley and Senate colleague Jon Tester of Montana expect to move forward in the next month with bipartisan legislation that would clarify when paid leave is allowed and "fill the void" that has existed for decades in terms of leave policy.

"This kind of leave shouldn't be a crutch for management to avoid making tough personnel decisions or a club to be used against whistleblowers," said Grassley, whose bill will differ from previous efforts that were agency-specific.

The concerns would appear government-wide. In October 2014, the Government Accountability Office (GAO) reported that federal agencies spent $3.1 billion from fiscal 2011-2013 on salaries for employees on administrative leave.

Because no uniform policy is set in law or regulation, agencies have functioned with broad discretion in setting and enforcing administrative policy for the last 50 years. This has contributed to what the Iowa senator describes as a "Wild West environment among agencies on paid administrative leave."

Following the GAO report, Grassley and then-House Committee on Oversight and Government Reform Chairman Darrell Issa sent letters to 17 agencies and one agency inspector general seeking a full accounting of why individuals were placed on leave. The information provided by the VA and DHS was so incomplete that it merited two additional requests, made in recent weeks.

In May, White House Office of Personnel Management Director Katherine Archuleta issued a memorandum informing agency heads that it would begin implementing a GAO recommendation to collect information from payroll providers in the near future and to make changes to the payroll data standards.

Extended and costly use of paid administrative leave is not a new phenomenon, but the abuse has exploded since 2001 when Grassley first demanded the Internal Revenue Service explain why it had permitted employee Aucqunette D. Cunningham to be placed on administrative leave for three years -- though she had been indicted, convicted and sentenced for accepting three bribes totaling $725 in 1999 and 2000 in exchange for illegally disclosing tax-return information.