Tax cuts for big business are in doubt with the Greens confirming they will block a reduction in the company rate which is due to start in July next year.

The Government intends to cut tax for small business by 1 per cent from July this year and reduce the company tax rate generally from July next year.

Greens leader Bob Brown says his party will support cutting company tax for small business as planned this July, but will not support wider tax cuts from next year.

Earlier on Tuesday the Opposition confirmed it would not support the tax cuts because they are linked to the mining tax.

Senator Brown says the Government will not have the numbers to make a general company tax cut because neither the Greens nor the Opposition will vote for it.

"The Greens have made it clear, I've made it clear since March last year that we would oppose the corporate tax cuts," he said.

"That's $2.4 billion that should be going to health and education and high-speed rail and the government services which instead under this government legislation will go to the big corporations."

The Federal Government says it will release a draft version of its bill to cut company tax on Wednesday and the actual bill will be introduced to Parliament during budget week in May.

Treasurer Wayne Swan is trying to pressure the Opposition, saying Coalition Leader Tony Abbott would prefer to give a tax cut to super-rich mining magnates and is refusing to help 2.7 million small businesses.

Finance Minister Penny Wong told ABC's 7.30 that the Government is committed to providing business tax cuts and a rise to compulsory superannuation from the revenue of the mining tax.

"The people who will guarantee they'll vote against tax cuts for small business and tax cuts for the broader economy are, of course, Mr Abbott and his colleagues in the Senate," she said.

"What they can guarantee - the only thing they can guarantee - is that they're there to protect the profits or wealthy miners. It's a very wrong-headed way of approaching this issue."

An Opposition spokesman says Mr Abbott has promised a modest cut to company tax that is not funded by the mining tax.