T-Mobile US and Sprint pushed back the deadline for completion of their proposed merger, as regulators continued to weigh the merits of the deal a year after it was first announced.

In a filing with the Securities and Exchange Commission, the pair set a new 29 July, 2019 deadline for the transaction to close. The move came despite reassurances days earlier from T-Mobile CEO John Legere (pictured, right) that the deal is still expected to gain clearance in the first half of the year as originally planned.

The operators recently stepped up efforts to persuade officials at the Department of Justice (DoJ) and Federal Communications Commission to swiftly approve the transaction.

But Makan Delrahim, head of the DoJ’s antitrust division, told CNBC the agency is still reviewing the economic impacts of the tie up, particularly its effect on competition and 5G pricing.

“With 5G and other technologies, you’re going to be able to use that phone for more than just communicating with your best friend or texting…we want to be sure to encourage that, but ultimately, is there going to be a price effect when those two combine?”

Delrahim said the DoJ is waiting on additional information it requested from the operators, adding there is no set timeline for the agency to conclude its investigation.