SPRINGFIELD - A deal that would send rebate checks to most Illinois Ameren customers won its first official approval Wednesday night, despite Republican opposition.

A House panel voted 5-3 along party lines to approve a $1 billion package that would have Ameren and ComEd issuing rebates of varying sizes to all of their customers.

Now, the full House and Senate and Gov. Rod Blagojevich must approve the package before it can take effect. Technically, all of those things could happen Thursday, but the deal has been months in the making.

Republicans opposed the deal during Wednesday's hearing, saying that the $1 billion wasn't enough and that the state's attorney general shouldn't drop lawsuits against the utility companies.

Republicans also complained that Democrats kept them out of the negotiating process.

"It was my understanding that the door was open," state Rep George Scully, D-Flossmoor, said.

Even though Democrats control the state House and Senate, Republican opposition could block the deal's approval in the House.

House Speaker Michael Madigan, D-Chicago, suggested early Wednesday that opposing a deal that would send rebates to voters would be politically dangerous.

"And if there are Republicans, especially from the Ameren service territory, who are going to vote against rate relief, why I welcome them to do it," he said.

The deal came after threats by lawmakers to force the utilities to cut their rates. It includes provisions that could curb future rate hikes by changing the way the companies buy power to distribute to customers.

Democrats and the companies both say they agree to the new plan, even if the utilities thought their own old way of buying power was acceptable.

"I also know that in order to get compromise, I need to accept change," said ComEd President Frank Clark.

Along with the change and rebates in the tentative deal are provisions to help customers who fell behind on their bills after rates spiked in January.

First, all late fees would be waived through Oct. 1, though delinquents would still owe money they hadn't paid on their actual bills.

Also, Ameren has agreed not to disconnect anyone's power until Sept. 1 this year, at which point the shutoff process could begin.

"We're not going to go out on Sept. 2 cutting people off," said Ameren spokesman Shelley Epstein.

In future years, the utility agreed not to shut off power to all-electric customers from December through March, when people would need heat the most.

The legislation is Senate Bill 1592.