The US Department of Justice (DoJ) and Federal Communications Commission (FCC) slammed an attempt by state legal officials to block T-Mobile US and Sprint’s proposed merger, warning the effort could jeopardise consumer benefits secured during their regulatory reviews.

State attorney generals opposing the deal have asserted the merger would lessen competition and ultimately harm consumers.

In a court filing, DoJ and FCC said they already “secured relief they determined would address the merger’s potential anticompetitive effects and yield substantial benefits to consumers”. The regulators urged the court to “give due weight and consideration to the judgments of the DoJ Antitrust Division and the FCC”.

“The litigating states must prove that a permanent nationwide injunction is necessary even though it will negate the relief already secured, and in the interest of the public even though it will prevent consumers from benefitting from that relief,” they wrote.

Under conditions set by DoJ and FCC, the operators would be forced to divest spectrum and other assets to Dish Network to help create a new national competitor.

Trial arguments in the case began 9 December and are expected to conclude by 23 December.