MSPs backed legislation that will mean people with a disposable income of £82 a week will have to make a contribu- tion towards the cost of their defence.
Defence solicitors had previously gone on strike over the changes, which will also see them collect the money instead of the Scottish Legal Aid Board.
About 40 solicitors gathered outside Holyrood yesterday to protest against the legislation.
For the Liberal Democrats, Alison McInnes said: "This bill is a blunt instrument – we could be faced with the prospect of more people being forced to represent themselves in court, lacking the crucial tools to do so effectively.
"We will risk sending more innocent people to jail. That is not in the best interest of justice or a fair society. The Justice Secretary has risked irrevocably harming access to justice in order to cut around £4 million out of a £150m budget. I don't think that's a price worth paying."
But Justice Secretary Kenny MacAskill insisted: "The Scottish Government believes it is right and proper that those who can afford to pay towards the cost of their legal defence costs do so.
"While I would rather not be reducing the legal aid budget, expenditure on legal aid in 2011/12 was £157.3m, which was, despite savings, the second highest on record. There is no endless pot of public cash and the current legal aid scheme simply cannot be maintained without making savings."
Labour voted with the SNP on the new income limit despite concerns that the overall Bill remains "bad".
Malcolm Chisholm, Labour MSP for Edinburgh Northern and Leith, said the legislation was driven entirely by finance, adding: "The Cabinet Secretary has been forced to modify a very bad bill so it ends up simply as a bad bill. That doesn't alter the fact it still is bad."
Tory MSP Annabel Goldie said: "I'm glad the Cabinet Secretary has yielded to his metaphorical beating over the head and improved what was a poor situation and made it somewhat better."