About 425 workers at Millstone Power Station began voting Wednesday and will continue voting Thursday on joining the International Brotherhood of Electrical Workers.

But the outcome of the election won't be known for some time, as the ballots probably will not be counted when voting is done, according to officials at the federal agency responsible for regulating union activity and worker rights.

Both the IBEW and Dominion Resources, owner of the nuclear power plant, have asked the National Labor Relations Board in Washington to review a local NLRB decision in April that the bargaining unit should include these workers.

Until the board in Washington either declines to hear the appeal, or makes a decision, the results are likely to be on hold, said Jonathan Kreisberg, regional director of the Boston office of the NLRB. The Boston office covers Connecticut. He said how long the board in Washington might take to rule is unknown.

The IBEW tried to organize the power plant once before, in 2002, and the vote was 199 for, 333 against. In this election, the workers eligible to vote are from fewer departments: operations, outage and planning, maintenance, nuclear site services and training department workers are being given the choice to join.

Millstone spokesman Ken Holt said this time, the company asked that about 800 of the 1,080 workers in Waterford be included in the bargaining unit.

"We believe all [non managerial] Millstone employees should be able to vote," Holt said, because the company believes the departments are highly integrated.

The company would prefer to continue operating without a union, however.

"Dominion respects the rights of its employees to organize, but we believe the best way to move forward is in a non-union environment," Holt said. He said without a union, there's more room to collaborate on an individual basis.

Kreisberg said that while "unions always say that the employers are trying to pack the unit to make it harder to win," that was not a factor in his decision.

Workers at the plant involved in the push to unionize did not return calls for comment, but one worker who declined to give his name said the desire to unionize was partly because of concerns over worker safety.

"We have a very safe work environment at Millstone," Holt responded. "Safety is our No. 1 priority." He said the last accident that caused a worker to miss any time at work was more than a year ago.