The clock is ticking down on the final parliamentary sitting week ahead of the budget, and the Federal Government's centrepiece — company tax cuts — still hang in the balance.

The 10-year Enterprise Tax Plan would see the company tax rates cut to 25 per cent for all businesses.

It would cost $48 billion, but the Government argues it would keep Australia internationally competitive and attract more foreign investment.

Labor and the majority of the Senate crossbench do not support the cuts, powerful crossbencher Senator Nick Xenophon has issued a further ultimatum.

"Unless the Government sorts out the energy crisis that grips this country … then I'm not inclined to support any company tax cuts for businesses with a turnover in excess of $10 million," Senator Xenophon, whose team controls three votes in the Senate, said.

"It's been devastating for my home state of South Australia and it will be like a contagion for the rest of the country with the closure of Hazelwood in the coming days," he said.

"The energy crisis has to be the Government's number one priority."

Senator Derryn Hinch has also vowed to block the tax cuts for the top end of town.

He said he had told the Government he would only support cuts for businesses with a turnover of up to $10 million.

Other crossbench senators share that position, which means the Government could likely pass tax cuts for smaller businesses.

Labor, the Greens and Senator Hinch are likely to vote with the Nick Xenophon team to block the cuts to big business in the Senate.

If the government wants to pass some company tax cuts, splitting the bill may be the only way to do it.