THE state's business community has called for a raft of last-minute changes to the WorkCover Bill as unions rally against the legislation on the steps of Parliament House on Tuesday.

More than 1000 construction workers are expected to protest, demanding the State Government abandon its plans to change the WorkCover system.

The rally is part of a targeted campaign against the State Government's WorkCover Bill, which unions say is unfair to injured workers.

Business SA, however, presented the Opposition with 17 proposed amendments to the Bill late yesterday, which included a reduction in the maximum weekly benefit payment.

The proposed amendments, which reduce employers' responsibilities for injured workers, have infuriated the unions.

Business SA director of employer advocacy programs David Frith said the amendments were proposed because the organisation believed improvements to the Bill were needed.

"Business SA has maintained from day one that we support the Bill but from day one we said it was not perfect," he said.

Construction Forestry Mining Energy Union state secretary Martin O'Malley said the Government's proposed laws were "bloody disgusting", leading to a march from Victoria Square at 10.30am. A rally will be held at the conclusion of the march at 11.30am.

"From the CFMEU's position we don't want any of the changes," Mr O'Malley said.

"We say that if there is a problem with the unfunded liability put it back to where the cause is – put it back on the employers. Increase their levies, don't reduce them."

Mr O'Malley said unionists would demand that injured workers' weekly entitlements be retained, common law rights be reinstated and protection for long-term injured workers continued beyond 30 months.

"It's going to be bloody horrible for the unions to clean up the mess left behind by these changes," he said. Construction worker Duncan McKay, 45, of Goodwood, said he felt betrayed by the Government.

"I have supported Labor all my life and I never thought I would be marching against a Labor Government over something that affects workers and families so much," he said.

The Liberals had not decided whether to support the Bill.

Opposition Leader Martin Hamilton-Smith yesterday said Business SA's proposed changes would stall the passage of the laws.

"Late yesterday we received a request from Business SA for a raft of amendments," he said.

"The late change of position by the business community is confusing the picture."