T-Mobile and Sprint have competed fiercely with each other, and with their larger rivals, AT&T and Verizon. If it has been an unpleasant experience for the companies, their customers have benefited. Since 2009, the average cost of mobile service has fallen by roughly 28 percent, according to the Labor Department. The companies also have sought to one-up each other with new products, more flexible contracts and better service. The market worked.

Federal regulators have come to evaluate mergers solely on the basis of whether consumers will benefit. This deal does not meet the test. It should have been obvious to regulators that T-Mobile’s promise not to raise prices for three years does not bode well for the fourth year.

A group of state attorneys general, led by Letitia James of New York and Xavier Becerra of California, has sued to block the merger, arguing that low-income consumers who buy prepaid wireless plans are particularly likely to suffer from higher prices. T-Mobile’s Metro PCS brand and Sprint’s Boost Mobile brand are major competitors in that market.

The government should also be paying attention to a host of other consequences.

The companies say their union will allow increased investment in technology, especially the costly build-out of a 5G network to allow even more data at even higher speeds. But T-Mobile could make those investments on its own. Indeed, studies show that corporate concentration actually reduces the pace of innovation, and of economic growth, for the obvious reason: Companies don’t try as hard when they’re not motivated by fear.

Corporate mergers also are slowing wage growth, by reducing competition for workers. And larger companies exert greater political power. American antitrust law was created to prevent the concentration of political power — an objective that deserves to be revived. It is odd that the Trump administration, which has expressed concern about the market power of tech companies, is willing to sanction the creation of yet another technology behemoth.