Iemma's plans to sell-off parts of the power sector will go before NSW parliament on Thursday, with the proposal's fate likely to be decided by the opposition.
Liberal leader Barry O'Farrell and Nationals leader Andrew Stoner are yet to declare their party's intentions on how they'll vote on the plan.
A number of Labor MPs have already declared they will cross the floor in the hope of defeating the legislation.
Iemma said he would not delay the vote if he didn't have the numbers, and would instead have to seek alternatives to secure the state's electricity needs.
"There's no plan B," Iemma told reporters.
"We'll have to deal with the consequences of this having been defeated and respond. It's not going to be a case that we're going to deferring this and coming back.
"The time to act is now."
The first vote will take place in the upper house, where the government does not have a majority, with Treasurer Michael Costa to make amendments to the legislation following a review of the sell-off by the state's auditor-general.
Iemma on Wednesday denied this was a tactic to avoid embarrassment by having the legislation defeated in the lower house, where Labor has the numbers but could lose due to dissenting ALP MPs voting against his plan.
"You can read nothing into the fact that it's going into the upper house at all," Iemma told reporters.
Iemma said Costa had not issued a financial ultimatum to Labor MPs considering voting against the sell-off.
Costa was reported to have issued the warning at a meeting of Labor branch delegates as the government pushed for support for the privatisation plan.
"I rang the treasurer and he flatly denies it. Absolutely not true," the premier told reporters.
Iemma would not be drawn on what consequences Labor MPs who voted against the government would face.
The premier on Wednesday took out full-page newspaper advertisements to set out reasons for the controversial sell-off .
In his open letter to the people of NSW, Iemma warns that "without new investment now, we face potential blackouts".
However, Stoner said the threat of blackouts was "crap".
Stoner, who on Tuesday stated he personally opposed the sell-off, said privatisation would not secure NSW's power supply.
"I think that's crap, frankly," he told Macquarie Radio on Wednesday.
"What we saw in Victoria was that state move down the privatisation path, I think about a decade ago, and that state actually faces shortages of baseload power earlier than NSW will."
