The FCC has started formal proceedings for its review of Verizon Wireless’ multi-billion dollar purchases of AWS spectrum from a group of cable companies that purchased the spectrum five years ago but never realized their plans to use it.

The agency opened a docket for the transactions late Thursday, WT Docket No. 12-4.

Verizon submitted applications with the FCC to transfer control of the AWS licenses on Dec. 21.

The FCC said it has not yet accepted the applications for filing. When it does, the agency will set out a formal pleading schedule for the deals.

The Department of Justice is also reviewing the transactions, a standard development for large acquisitions.

The FCC uses a self-imposed 180 deadline to time its review of transactions, but has been known to pause so-called shot clock during complicated proceedings. It stopped the clock on AT&T’s $1.9 billion purchase of Qualcomm’s Flo TV spectrum last fall to study “related issues” to the operator’s now failed attempt to buy T-Mobile USA.

Verizon announced last month that it was paying $3.6 billion for a huge swath of AWS licenses from Comcast, Time Warner Cable and Bright House Networks and later announced a separate $315 million deal to buy another chunk of AWS spectrum from Cox Communications. The combined licenses cover about 287 million people nationwide.

The four cable operators bought the spectrum during the FCC’s 2006 auction, when they placed a winning bid of $2.4 billion for the airwaves. Cox eventually split off from the group to pursue its own wireless ambitions but later gave up on the plan. The other cable operators never deployed services on their spectrum.

Verizon plans to use the spectrum to add capacity to its LTE network, which runs in its nationwide footprint of 700 MHz spectrum.

The FCC’s review will give groups opposed to Verizon’s spectrum grab a chance to make their case. The deals are likely to face opposition from the Rural Cellular Association, which last month issued a statement voicing concern about the transactions’ impact on competition.

“The proposed spectrum sale would exacerbate the current difficulties competitive carriers have seeking data roaming agreements, obtaining devices, and entering the marketplace,” RCA President and CEO Steven Berry said in a December statement.

Verizon has filed a statement with the FCC arguing the deals were in the public interest as part of the application it submitted last month.