Senate Finance Committee leaders have proposed tough laws to deter abusive corporate tax shelters by imposing heavy fines on those who promote sham transactions in efforts to evade taxes. The fines would not be waivable and would increase in penalties on the promoters of the transactions. The proposal would create a new class of tax shelters that would enforce a penalty of 40 percent of the tax evaded. Tax shelters, considered highly abusive devices, rely on techniques that have already been found to be fraudulent, lacking economic substance, and having no business purpose other than tax evasion. The only problem with the proposal, according to Peter L. Faber, the New York tax attorney who has been fighting to get abusive tax shelters under control, said the proposed laws are aimed at abusive tax shelters that have no economic substance, yet they do not define what economic substance means.