A late-night debate in the Senate on proposed changes to the Racial Discrimination Act has been described as "filibustering" by the Opposition.

Key points: Government wants to replace words "insult", "offend", "humiliate" with "harass"

Government wants to replace words "insult", "offend", "humiliate" with "harass" It does not have the numbers to pass changes

It does not have the numbers to pass changes Labor, the Greens, some of the crossbench killed off amendments after seven hours of debate

The Government had extended the Senate's sitting hours so it could deal with two key pieces of legislation: changes to the act and the Government's cuts to company tax rates.

The Government had wanted to replace the words "insult", "offend" and "humiliate" in section 18C of the Racial Discrimination Act with the term "harass".

On Thursday evening it became apparent the Government did not have the numbers to pass the changes, but the debate continued.

After seven straight hours of discussion, Labor, the Greens and some of the crossbench killed off the amendments.

It means the wording of section 18C of the Racial Discrimination Act will not change.

The Senate then continued debating process changes to the Human Rights Legislation Amendment Bill, the majority of which were uncontentious.

After another hour of discussion, Labor Senator Sam Dastyari accused the Government of trying to kill time.

"Let's just be clear what's going on here," he told the Senate.

"The Government is filibustering on its own bill about watering down race hate laws so that it can cut a deal on giving big business tax cuts."

"It's 11.30pm — you still don't have a deal."

The intention was for the Senate to sit until both issues had been dealt with, but just after midnight the Government suspended the sitting without a mention of the second item on its agenda.

Company tax cut negotiations continue

The suspension means the Government is yet to strike a deal on its company tax cut legislation with the Senate crossbench.

Thursday was supposed to be the final sitting day before the Government hands down its budget in May.

But with a key part of the budget still in limbo, the Government has extended the sitting hours of both houses into Friday to try to pass the legislation.

The Government's 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 legislation in its current form.

The negotiations are about the size of the businesses that should receive a tax cut.

The key players are the Nick Xenophon Team, which so far has maintained it will not support cuts for businesses with a turnover of more than $10 million a year, while One Nation is urging the Government to cap it at $50 million.

The Government looks almost certain to have to split its bill and pass cuts for smaller businesses before deciding whether to re-prosecute the case for tax relief at the top end of town after the budget.