Calling it the largest civil penalty every paid to the U.S. Treasury to resolve an FCC investigation, the FCC announced that Straight Path Communication and Verizon Communications have paid about $614 million to settle a spectrum-related investigation.

The announcement came just hours after Verizon, after outbidding AT&T, closed its acquisition of Straight Path, a deal that gives Verizon access to 39-GHz and 28-GHz millimeter wave spectrum that will be used for coming 5G networks.

RELATED: Verizon Outbids AT&T for Straight Path

The probe stems from a January 2017 settlement that Straight Path stuck with the FCC's Enforcement Bureau -- prior to its sale and transfer of licenses to Verizon -- over claims that Straight Path violated the FCC’s buildout and discountenance rules related to about 1,000 licenses in the millimeter weave spectrum bands.

The settlement, the FCC added, required Straight Path to sell its licenses and remit 20% of the overall proceeds of the transaction to the U.S. Treasury. 

Verizon and Straight Path inked a deal on May 11, 2017, to transfer the licenses, and on Jan. 18 the FCC’s Wireless Telecommunications Bureau approved the transfer, the agency said.

Under the deal, Verizon agreed to acquire Straight Path for $184 per share, an all-stock deal that represents an enterprise value of about $3.1 billion.

The $614 million is in addition to the $15 million that Straight Path previously paid to the U.S. Treasury, and its earlier relinquishment of 196, or 20%, of its licenses to the FCC that were not included in the Verizon deal.

In an announcement with potential 5G spectrum implications, Straight Path Communications said its board has determined that an unsolicited bid from a “multi-national telecommunications” is superior to the one it had already received from AT&T.

The new bid is for 100% of the issued and outstanding shares of Straight Path for $104.64 per share, or an enterprise value of $1.8 billion. AT&T had already put in a bid of $95.63 per share, reflecting an enterprise value of $1.6 billion, that would be paid using AT&T stock.

Straight Path shot up $14.68 (13.24%) to $125.57 each in late morning trading Tuesday. 

Straight Path didn’t identify the unsolicited bidder by name,  but Reuters reported on April 13 that Verizon was thinking about coming in with a larger, counter bid.

RELATED: Straight Path Stock Spikes on Verizon Bid Report 

Straight Path is a holder of 39 GHz and 28 GHz millimeter wave spectrum that could come in handy for 5G deployments.

RELATED: AT&T Eyes More 5G Spectrum with Straight Path Buy

Straight Path said it has notified AT&T that it has five business days to negotiate a possible amending to its agreement that matches or exceeds the new one. Straight Path said the new bidder  has stated that its offer will remain outstanding until 11:59 p.m. ET on May 3, 2017.

Under the AT&T deal, Straight Path is required to pay a $38 million break-up fee to AT&T if the deal is scuttled.