After more than two years, the Treasury Department has proposed rules to implement the new minimum tax on companies’ book income. Now comes the hard part.

The regulations, which Treasury issued last month, would govern how the corporate alternative minimum tax is applied and calculated. CAMT, enacted in 2022, requires big companies to pay at least 15% in taxes on the income they report on their financial statements—a crackdown on companies that have been able to pay little or nothing in the past by taking advantage of tax breaks and tax-planning strategies.

The proposed regulations run to more than 600 pages, and set up a highly complex regime for companies that fall under CAMT. Tax professionals and companies continue to pore over the rules, to see what kind of effects they’ll have.

Bloomberg Tax senior reporter Michael Rapoport spoke with Monisha Santamaria, a principal in KPMG LLP’s Washington National Tax practice about the complexity of the CAMT regulations; some notable aspects of the rules; how CAMT will affect more than just the 100 or so companies that Treasury says will have to pay it; and the chance for companies to persuade Treasury to revise its plans.