Two Republican senators raised concerns Wednesday about Department of Veterans Affairs employees who spend all their federally paid work time on union activities at a time when the agency is trying to plow through a massive claims backlog.

Sen. Tom Coburn (Okla.) and Sen. Rob Portman (Ohio) questioned the practice in a letter to VA Secretary Eric K. Shinseki, asking how many employees spend 100 percent of their paid time on union-related work — known as “official time” — and whether the department has had to hire new employees to cover their formal job duties, among other details.

The senators noted that 188 VA employees worked entirely on official time between January 2012 and February 2013. That number also was contained in documents that the conservative group Americans for Limited Government obtained through a Freedom of Information Act request.

“It is essential that every VA employee is dedicated 100 percent to our nation’s mission of providing the best healthcare to our veterans in a timely manner,” the letter said. “Federal employees not serving veterans during official time could lead to the failure of VA’s top goals, and the well-being of those who have sacrificed in the service of our nation could be compromised.”

Federal labor law allows official time for union activities such as collective bargaining, representing workers in grievances and disciplinary matters, and communicating about workplace issues. It does not permit pay for internal union business or handling matters unrelated to employment conditions.

The law does not limit the amount of paid time that federal workers can spend on union activities. Instead, it allows agencies and the unions to work out agreements concerning what is “reasonable, necessary, and in the public interest.”

In a 2011 report to Congress, the Office of Personnel Management described official time as “a critical component of the carefully crafted collective bargaining system that Congress created for the Federal Government.”

Government costs for official time increased nearly 12 percent in 2011, compared with the previous year, according to an OPM report.

The union that represents VA employees contested the notion that official time has inhibited the agency from handling its caseload.

“These employees help mitigate workplace disputes and personnel matters that often hinder the effective delivery of services,” said Alma Lee, president of the American Federation of Government Employees’ VA council. “Having dedicated employee representatives on hand to address labor-management issues as they occur benefits the agency and its customers.”

The VA in May increased overtime to help deal with the department’s claims backlog. House Democrats have introduced legislation to help improve the numbers, and the White House has proposed a 13.6 increase in VA funding to handle veterans’ benefits.