COLUMBUS, Ohio (AP) -- Exelon said Tuesday it has ended its $7.4 billion, all-stock bid for power generator NRG Energy.

Chicago-based Exelon Corp. withdrew its offer shortly after NRG shareholders rejected a proposal that would have expanded NRG's board, preferably with new and existing seats going to people that would support the takeover. Princeton, N.J.-based NRG has rejected two offers for the company from Exelon, calling them undervalued.

The deal would have created the nation's largest power generator, a company big enough to provide electricity to about 45 million homes.

NRG said a preliminary vote count at its annual meeting showed shareholders voting to re-elect the company's nominees to the board over a slate of nominees from Exelon. At the same time, they also rejected Exelon's bid to expand the board and fill the five spots with its nominees.

NRG did not release a vote count. It said final results will be released in August.

"NRG stockholders understood that this vote was all about value and they voted overwhelmingly to send a message that Exelon's current offer was unfair to NRG stockholders," David Crane, president and CEO, said in a statement.

Crane said the company will continue to evaluate offers from Exelon and any other company.

Exelon said in a statement that after bidding twice for NRG, it was unwilling to sweeten its offer again.