The Scottish Government is being urged to use new legislation to send a "clear message" to companies which dodge paying tax.
Trade unionists are calling for a new Bill on public procurement to ban tax-dodging firms from winning public contracts.
The Procurement Reform Bill has been put forward by the Government in an attempt to improve the way the public sector buys goods, works and services.
Leaders at Unison, a union for public service workers, argue that the time is right for legislating to prevent firms which do not pay their taxes from winning public contracts.
Unison highlights a Christian Aid survey which found that 80% of people are angry about firms not paying their fair share of taxes, with a third of them boycotting the companies because of it.
Dave Watson, head of bargaining and campaigns at Unison, said: "There is enormous public anger over companies that don't pay their fair share of tax.
"The timing of this Bill is perfect for the Scottish Government to respond. We are suggesting that the Bill should send out a very clear message.
"As Chief Secretary to the Treasury Danny Alexander has said, 'Taxpayers' money should not be funding tax dodgers'."
A Scottish Government spokesman said: "Although most taxes are currently the responsibility of Westminster we expect all businesses and individuals working in Scotland to meet in full their tax liabilities.
"Tax evasion is illegal, and we have made it clear that we will take the toughest line on tax avoidance."
