Political funding rules need to be overhauled to tackle the impact of “dark money”, the Scottish Greens have said.
The Greens want to see increased transparency and stricter regulation on how parties are funded.
They are calling for new laws to ensure full disclosure on exactly where donations to political parties come from.
Current rules do not place any limit on the size of donations to parties or individual politicians.
However the regulations require donations to be made from a “permissible source”.
Donations can only be made from individuals who are on the UK electoral register, while companies and organisations such as trade unions must be registered in the UK.
Scottish Green co-leader Patrick Harvie said: “Our politics should never be for sale.
“Yet there is dark money and a cast of dodgy donors right at the heart of Westminster and this election.
“When billionaires buy into political parties, they are buying influence.
“The Tory Party has long been a vehicle for vested interests and those that benefit from a broken status quo, but Labour are now fast becoming the party of the billionaires.
“In the long-run we need to move to a fair system of state funding of political parties to create a truly level playing field, but there are important steps we can take right now.
“We need far stricter limits on donations and campaign spending, and tougher transparency and enforcement rules.
“Our politics needs to represent the voices of normal people and families across our country, not the big businesses and cast of millionaires that are funding our biggest parties.
“It is not an accident or a coincidence. It is the end result of a fundamentally undemocratic system that has put far too much power in the hands of a small number of wealthy cronies.”