The planned takeover of Alliance Data Systems ( ADS) by Blackstone Group ( BX) has probably fallen apart. Alliance said Monday that the Office of the Comptroller of the Currency, a banking regulator, has put conditions on the more than $6 billion deal that Blackstone is unlikely to meet. Blackstone told Alliance the OCC is "demanding that extraordinary measures be taken" that "represent operational and financial burdens," and that it isn't willing to satisfy the requirements being set forth. Additionally, Alliance said, "Blackstone also expressed its belief that alternative solutions that would be acceptable to Blackstone would not satisfy the OCC, and therefore that further negotiations with the OCC would be futile." Shares of Alliance plunged 41% to $38.75 on the news. Alliance is evaluating "possible courses of action" and said it will do what's best to protect the interests of the company and its stockholders. Last May, Blackstone agreed to pay $81.75 a share for ADS, a transaction-services company, but doubts had been lingering for months about whether the pact would actually be completed.