I just bought a copy of Alan Crawford's Thunder on the Right, a book published in 1980 which details many of the sordid details of the rise of movement conservatism. I'd had the book out from the library a few years back but decided I really needed my own copy for reference. Crawford himself was a disillusioned conservative who decided to blow the whistle, so it's full of inside dirt.
According to Crawford, ALEC started off as an alliance of conservative state legislators, put together as a research clearing-house by an Illinois Republican activist who became its first executive director. But then the Heritage Foundation swooped in:
When Mrs. Bartnett began to solicit funds, a representative of the Heritage Foundation independently contacted Richard Larry, an employee of the Sarah Scaife Family Charitable Trusts. ... Obtaining the needed funds from the Scaife Foundation, the new group dismissed Mrs. Bartlett from her position (she subsequently sued the organization, which settled out of court), and moved it to Washington, D.C., from Chicago, and added to its board Weyrich, Frank Walton of the Heritage Foundation, and Edwin Feulner. Mrs. Bartnett asked Weyrich, "'why Scaife wanted to invest $80,000 in ALEC' and he told me: 'Juanita, ALEC is the only state legislative organization in the country--of our persuasion--which has a 501-C-3.' ... He assured me that he was not trying to 'buy' the state legislators, but the possibility of some campaign funding for them was there." ...
The Weyrich faction prevailed, and the organization, funded by the Scaife Foundation, moved to Washington where it became an adjunct of the growing New Right network. "They really wanted to get rid of me because I knew what they were trying to do with the organization and they knew I would have no part of it," Bartnett told me. She concluded, from examining records of telephone calls and methods of payment within the organization, that they wanted to use the tax exemption status as a shelter under which to conduct political activity. "They were trying, when they fired me, to turn the organization into an arm of the Reagan campaign, by funneling tax deductible contributions through ALEC to be used to finance pro-Reagan activities."
Crawford also noted that in 1978, ALEC had sent out materials urging state legislators to reject the Washington, DC voting rights amendment -- even though it had assured the IRS it "would make no attempt whatsoever to oppose or support pending legislation other than providing research material to member legislators as regards model legislation."
So basically ALEC was born out of the Heritage Foundation's desire to have a tax-exempt organization to use for political money-laundering and as a means of putting pressure on Republican state legislators. I don't know if they're still violating their tax status, but it might be worth looking into.