WASHINGTON — For decades, lawmakers helped home-state manufacturers lower the cost of imported materials by crafting tiny bills that reduced or eliminated tariffs on products that range from massive factory equipment to vats of industrial-strength chemicals.

Every year or two, hundreds of these duty suspensions would be rolled into one big miscellaneous tariff bill – an MTB, in Capitol Hill parlance -- and passed. Such legislation was so routine, it was approved by unanimous voice vote.

But like so much else in Washington these days, the commonplace has become controversial, and these targeted tax breaks have come under scrutiny.

The scrutiny has opened a rift among Republican lawmakers. They like tariff reductions as tax cuts, but some who favor a flatter income-tax system and a "level playing field" for businesses see miscellaneous tariff bills as congressional pork doled out to favored companies with lobbyists to push for the duty suspensions and campaign contributions for senators or representatives who get them.