IRS officials, according to the GAO, said the agency has not issued guidance to clarify the issue because of "competing priorities."

As a result, 401(k) plan provider practices vary. "Some providers withhold taxes when transferring savings to states while others do not," GAO said.

"This makes the IRS less likely to collect federal income taxes that may be due if transfers are taxable events," GAO said, adding that the IRS also needs to ensure that individuals who claim 401(k) savings from a state can roll over these savings to other tax-deferred retirement accounts after IRS' 60-day deadline.

IRS allows individuals to roll over savings after 60 days for several reasons, none of which include claiming 401(k) savings from a state, GAO said.

Account owners who are unable to roll over their reclaimed savings "forgo the opportunity to continue investing the funds on a tax-deferred basis," GAO maintains.

Millions of dollars in retirement savings are transferred to states as "unclaimed property, only some of which is later claimed by owners," the GAO explains.

As workers shift jobs and leave behind retirement savings accounts, retirement savings are more likely to be unclaimed. Stating that an exact figure is not known, unclaimed retirement savings in the United States have been estimated to exceed $100 billion, GAO states.

Fred Reish, a partner at Drinker, Biddle & Reath in Los Angeles, adds that the GAO report covers not only unclaimed IRAs but uncashed checks. "If there isn't any activity with regard to an IRA for a period of years, and perhaps the IRA trustee (eg., a bank) can't locate the IRA owner, the money escheats to the state."

Regarding uncashed checks, "plans send out checks as requested distributions, forced distributions of less than $1,000, and minimum required distributions," Reish explained. "In some cases, those checks are never cashed. After a period of time, the check will escheat to the state as unclaimed property. Both of those happen more than you would think."

In fact, of the 22 states responding to a GAO survey, 17 states provided data indicating that $35 million in unclaimed retirement savings was transferred to them from employer plans and IRAs in 2016.

Assets and uncashed checks from employer plans (such as 401(k) plans) were the most common form of retirement savings transferred to states. After funds are transferred, owners can claim their savings from the state.

According to the 15 states providing data on this, owners claimed about $25 million in retirement savings in 2016: $601, on average, from 401(k) plan checks, and $5,817, on average, from traditional lRAs, GAO said.