The ban on rich foreign donors funding political parties should be extended to Northern Ireland, Friends of the Earth has said.
With David Cameron promising more transparency on party finances in the province, the environmental pressure group is challenging the prime minister to end the anomaly where parties on the island of Ireland can still obtain money from abroad.
After their 1997 general election victory New Labour outlawed the practice of corporations and foreign supporters funding parties in the UK. However, Tony Blair excluded Northern Ireland from the legislation because parties central to the peace process, principally Sinn Féin, raised millions of dollars mainly from Irish Americans in the US.
Cameron has written to the Alliance party's East Belfast MP Naomi Long informing her that UK-based donors will be named after January.
At present there is a veil of secrecy over donations from local supporters in Northern Ireland because of fears donors could be targeted by terrorists as was the case during the Troubles.
But Friends of the Earth has called on the government to go one step further and outlaw donations to Northern-Ireland-based parties from abroad.
James Orr, Friends of the Earth's director in Northern Ireland, said: "We find it very hard to accept that people or corporations outside the UK or Ireland should be able to influence politics in Northern Ireland by paying political parties here."
Orr said the government's reluctance to move on the issues of both foreign donations and secrecy in Northern Ireland went against the prime minister's own demands for more transparency in the global economy at the G8 summit last month.
He added: "The Alliance party is to be congratulated for its efforts to shine a light on the murky world of donations to Northern Ireland's political parties. Transparency is vital if people are to have confidence that politicians are acting in the public interest, and not in the vested interests of their donors. It is unjust and indefensible that the government has chosen to deny the people of Northern Ireland the same rights to see who funds political parties as people in the rest of the UK. During the recent G8 meeting in Fermanagh, the prime minister made transparency a priority issue. It's a shame he doesn't feel it applies to a part of his own country.
"The legislation going through parliament is a step backwards and will make secret donations the norm. Previously, transparency was the default position and the government had to act to maintain anonymity for Northern Ireland donors. If the proposed changes are passed, anonymity will become the default, and the government will have to act to introduce transparency. The government is preparing to cement injustice and inequality in UK law."
Orr said this was one of several "troubling developments".
"Planning laws are being rewritten to curtail people's right to challenge planning decisions; the executive has decided to opt out of the new defamation law, so even a reasonable suggestion of funding impropriety could result in legal action; and petition of concern, a mechanism to prevent majoritarian rule in the assembly, is routinely being misused to block the democratic will of the assembly. Including the cementing of donor anonymity, Northern Ireland is facing the death of democracy."
Northern Ireland is the only area of the UK where political donations are secret. Elsewhere, the names of donors giving more than £7,500 are published but in Northern Ireland they are kept secret on security grounds. The position will be reviewed by the secretary of state in October 2014.