The decision, which has just been made public, could make the Christian Coalition, a highly influential constituency within the Republican Party, liable for 10 years' back taxes just as next year's presidential election campaign is hotting up.
This blow to the organisation follows the recent decisions by the Bank of Scotland and Laura Ashley to sever their ties with Mr Robertson because of his public remarks on homosexuals. The outcry over Mr Robertson's religious views underlined a sharp cultural difference between Britain and the United States, where Christian fundamentalism is a social and political force to be reckoned with. While he will receive compensation of several million dollars from the bank, its retreat bodes ill for his efforts to expand into Europe.
The US Internal Revenue Service (IRS) ruling was determined by what it judged to be the political nature of the Christian Coalition and the extent of its commercial and lobbying activities.
Founded by Mr Robertson in 1988, it has made substantial contributions to Republican candidates who endorsed its fundamentalist programme and supplied literature that was often distributed at churches by sympathetic pastors. Such was its influence that Pat Robertson himself became something akin to a power broker inside the Republican Party.
The IRS made its first ruling on the Christian Coalition's tax status last year, but agreed to keep the decision confidential pending an appeal. The coalition received notice in the past 10 days that it would lose the appeal.
The coalition is now to be restructured. While this has been dictated in part by the IRS ruling, it also reflects increasing internal difficulties and a weakening of the organisation's influence on the US political scene.
According to the coalition's spokesman, Mike Russell, the organisation will be split into two. The new Christian Coalition International will operate as a "for-profit" corporation, able to engage in party political activity, endorsing political candidates, making campaign contributions, and perhaps opening chapters abroad.
The other part would be named the Christian Coalition of America and restrict its work to non-profit "voter- education". Mr Russell said: "The organisation has been dramatically reshaped, but its mission statement remains intact and it will continue to do the things it has been doing since it formed, which is to recruit pro-family activists, draw people to the polls in record numbers for elections and educate people on the issues that affect families."
A force within the Republican Party that built on the Reagan-era return to Christian fundamentalism in politics, the Christian Coalition has watched its influence decline during Bill Clinton's presidency, both in the country - its income fell by more than one-third between 1996 and 1997, from $26m (pounds 16m) to $17m - and inside the Republican Party.
The rise within the party of less dogmatic and more pragmatic state governors - exemplified by George W Bush of Texas - is curbing the influence of the religious right and leading candidates for national office to temper their opposition to such issues as abortion. George W Bush is typical of the new trend, professing that while he personally opposes abortion, the country at large is not ready to accept a legal ban. At the same time, more people appear willing to speak out against groups such as the coalition. One seasoned critic, Barry Lynn of a group advocating a clearer separation of church and state, responded to the IRS ruling by saying: "The Christian Coalition is a hardball political machine that is masquerading as a religious group. The evidence is overwhelming that this organisation has been operating as virtually an arm of the Republican Party."
Even conservative groups appear to accept that the political influence of the religious right is in decline. John Whitehead, president of the Rutherford Institute, the conservative legal group that helped to fund Paula Jones's sexual harassment case against President Bill Clinton, said: "The Christian right has been potent for a while, but now it's going away."