The rail union believes the bill is on the right tracks

The bill has been drawn up by Socialist MSP Tommy Sheridan.

Holyrood's cross-party local government committee urged MSPs to throw out the bill after a "most comprehensive rejection" of its proposals last week.

The RMT said rail workers were supporting the move "in the interests of a fairer, more equal Scotland".

Modest incomes

Bob Crow, general secretary of the union, which broke its links with Labour in 2004, said: "Redistribution of income is a highly laudable objective which RMT supports and that's exactly what this bill delivers."

Mr Sheridan wants to see people who earn �30,000 a year paying 15% tax and those on �90,000 paying 20%, above their normal income tax.

He said people on an income of less than �10,000 would not pay.

Holyrood's local government committee said the tax would be unfair to people on modest incomes but the SSP said Scotland's poor had been let down.

A committee report said 400,000 poorer people were already exempt from council tax and a nationally set service charge would undermine local decision making.

It also said the tax would be difficult to collect.

This would be a progressive tax where the less an individual earns, the less they pay Tommy Sheridan SSP

Committee convener, Labour MSP Bristow Muldoon, described the dismissal of the proposal as the "most comprehensive rejection of any bill that's been brought before the Scottish Parliament since it was introduced in 1999".

However, Mr Sheridan has urged parties which have called for council tax to be scrapped - including the Lib Dems and the SNP - to back the bill's general principles.

He said it could then proceed to stage two when it could be amended in line with their own proposals for an income-based local tax system.

Mr Sheridan added: "This bill represents a great opportunity for the Scottish Parliament to make a real difference to the lives and disposable incomes of the low-paid and pensioners in Scotland.

"This would be a progressive tax where the less an individual earns, the less they pay."

Other trades unions, pensioners' groups and anti-poverty campaigners have supported the proposed changes.