Shares of spectrum holding company Straight Path Communications (STRP) shot higher Monday after the company disclosed that a rival suitor may top a $1.6 billion acquisition offer by AT&T (T) .

The mystery suitor told the company and its bankers that it is exploring an offer that would top AT&T's bid, Straight Path said in an SEC filing late Thursday after the market close, ahead of the long weekend. Speculation centered on Verizon (VZ) , after a Reuters report identified the telecom as the challenger, citing sources familiar with the matter. Verizon declined to comment.

AT&T last week agreed to pay $95.63 per share in stock for Straight Path, a 162% premium to the company's April 7 closing price. Shares of the target company jumped more than 13% to $103.70 on Monday morning on anticipation of a potential new deal and higher deal price.

Straight Path, which telecom and payments company IDT Corp. (IDT) spun out in 2013, owns a portfolio of licenses to millimeter wave wireless spectrum. The licenses cover high-frequency spectrum that telecoms plan to use for 5G wireless services, the coming generation of wireless technology designed to boost capacity and extend the Internet to medical devices, street lamps, cars and other machines and devices.

The company had been under pressure to find a buyer.

The FCC slapped Straight Path with a potential fine of $100 million in January for spectrum squatting, or failing to build out infrastructure to operate spectrum. Straight Path would pay an initial $15 million fine and another $85 million if it could not sell its spectrum by the end of the year. Additionally, the U.S. Treasury will take 20% of the eventual sale price as a civil penalty.

Straight Path hired investment bank Evercore to advise on a sale after the FCC fine.

AT&T, Verizon and others have all targeted millimeter wave spectrum as they plan to build out their 5G networks. 

In January, AT&T said it would buy FiberTower Corp., which has similar licenses. Verizon gained access to millimeter wave spectrum in its $1.8 billion purchase of the fiber network business of XO Holdings, which closed in February. Verizon can lease XO's spectrum with an option to buy the licenses.

Outside the large wireless companies, spectrum-hungry satellite TV company Dish Network (DISH) gained similar spectrum in a deal with EchoStar (ECHO) .

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