House of Representatives Speaker John Boehner said on Wednesday a U.S. Senate plan to extend long-term unemployment benefits retroactively "is simply unworkable" after a state officials group warned of implementation problems.

The National Association of State Workforce Agencies said in a letter that some states may find the plan's verification requirements too costly and onerous, and could try to opt out.

The bill's requirements "would cause considerable delays in the implementation of the program and increased administrative issues and costs," NASWA President Mark Henry said in the letter to Senate Majority Leader Harry Reid and Senate Republican leader Mitch McConnell.

The Senate is expected to vote in coming weeks on bipartisan legislation to renew the jobless benefits for the first five months of 2014 that would put an average of $300 per week into the hands of long-term unemployed workers. The checks would be retroactive to December 29, 2013.

For Boehner, whose House Republican caucus has shown little interest in the extending unemployment benefits, the letter from the state officials' group bolsters the case for opposing the Senate plan. He said it was "cause for serious concern."

Boehner said Republicans would still look at an unemployment benefits extension bill from Democrats that is "fiscally responsible" and helps to create more private-sector jobs.

"There is no evidence that the bill being rammed through the Senate by Leader Reid meets that test, and according to these state directors, the bill is also simply unworkable," Boehner said in a statement.

Reid's spokesman, Adam Jentleson said Democrats believe that concerns raised by the state officials are "resolvable" and urged Boehner to help craft solutions.

"It is hard to imagine Speaker Boehner simply walking away from the thousands of people in Ohio who lost their jobs through no fault of their own and need this lifeline to make ends meet while they continue to look for work," Jentleson said.

The $10 billion cost of the Senate extension measure would be offset by other savings, including allowing companies to apply accounting procedures for pension contributions that would boost their profit, resulting in increased federal revenue. It also contains a provision that would prohibit payment of unemployment benefits to anyone who has earned income of at least $1 million in the previous year.

Henry, who also serves as director of the Mississippi Department of Employment Security, said the state workforce agencies were not taking a position for or against the extended benefits but were pointing out difficulties in the proposed legislation, including the inability to verify whether beneficiaries met requirements that they sought work during the first few months of 2014.

Under normal circumstances, beneficiaries report weekly on their job search activities, but this has stopped in many states since the checks stopped flowing in January.

Antiquated computers that cannot be quickly reprogrammed represent a challenge and the "millionaire provision" is problematic because it is based on income tax return data, which unemployment agencies do not collect, Henry said.

Determining eligibility under this means-testing provision would cost states money and the proposed legislation provides no federal funds for this.