Two Democratic senators, concerned that the federal government is relying too heavily on a back-door mechanism to award sole-source contracts, are taking the issue to the White House.

In a letter to Anne Rung, the administrator of the Office of Federal Procurement Policy, the senators said they are growing increasingly alarmed with the use of so-called “bridge contracts,” which can be awarded without competition on a short-term basis to extend a contract if the agency isn’t prepared to issue a new one.

But Sens. Claire McCaskill (D-Mo.) and Tm Carper (D-Del.) said they fear that “when noncompetitive contracts are used frequently or for prolonged periods, the government is at risk of overpaying for goods and services.”

The letter follows a report, issued earlier this month, from the Government Accountability Office, which found that even though bridge contracts are supposed to be short-term, many were for extended periods, including a few that lasted for more than three years.

One Army bridge contract for computer support services was initially supposed to last a year but ultimately spanned 42 months. While most of the 73 bridge contracts reviewed by the GAO were less than $1 million, some were quitter lucrative, including one valued at $79 million.

And the GAO found that when the contracts were finally put out for bids, the competition in many cases led to a reduction in price. That, the GAO said, “highlights the urgency of ending bridge contracts as soon as possible, since these contracts are almost always sole-source.”

The GAO also found that the agencies, which included the Pentagon, the Department of Health and Human Services and the Justice Department, “had limited or no insights into their use of bridge contracts” and some lacked policies on how to use them.

Part of the problem stems from an inexperienced contracting workforce, the GAO found. Army contracting officials told investigators that “their overwhelmed contracting office also struggled to award new contracts in a timely manner.”

Air Force officials complained that “the majority of their contracting workforce had less than five years of experience, which contributed to significant delays in awarding follow-on contracts.”

In one case, an “inexperienced” contracting official failed to exercise an annual option for a contract, and allowing the contract to lapse, the GAO found. But no one noticed, and the Air Force contractor continued to provide logistics management service without a contract to or “five weeks before the mistake was realized.”

In a statement, Jamal Brown, the press secretary for the White House Office of Management and Budget, said the administration is committed to promoting competition in procurement.

“Since 2009, we have seen a significant reduction in the dollars spent with just one bid and an increase in the amount of dollars competed overall,” he said. “While there is a legitimate role for bridge contracts in helping to avoid lapses in service, agencies bear a responsibility to ensure this non-competitive authority is being used only to the extent necessary.”