Sources tell Reuters that Verizon (NYSE:VZ) is readying a bid to acquire Vodafone‘s (NASDAQ:VOD) stake in their U.S. wireless joint venture, Verizon Wireless.

The bid could total more than $100 billion, funded with both cash and Verizon shares. Verizon has not approached Vodafone over the deal yet, but is laying the groundwork to launch a bid. Both companies have previously discussed potential changes to the joint venture. Concerns over Vodafone’s potential tax bill from any buyout have emerged as a significant issue.

Verizon owns 55% of the nation’s largest wireless carrier and has long wanted to gain sole ownership of the business.

An unnamed Vodafone investor told Reuters that $100 billion was too low a bid to win a deal and that Vodafone was looking for a buyout price of between $125 billion and $130 billion.

Verizon has reportedly begin hiring financial and legal experts to advise it on the potential bid. Keeping the tax bill for the deal to under $5 billion was said to be a driving force in the way any acquisition would ultimately be structured.

Earlier this month, rumors circulated that Verizon would partner with AT&T (NYSE:T) on a complex bid to acquire both Vodafone’s interest in Verizon Wireless and Vodafone itself. Under the arrangement, Verizon would get full ownership of Verizon Wireless, while AT&T would purchase Vodafone’s overseas operations.

Shares of Verizon rose more than 1% in Thursday morning pre-market trading, while Vodafone climbed more than 2%.