Verizon Communications Inc. (VZ) debt holders are calling on the telecom giant to amend the terms of a debt exchange over fears it could acquire Charter Communications Inc. (CHTR) and put its credit rating at risk.

Last week The Wall Street Journal reported Verizon Chief Executive Lowell McAdam reached out to Charter executives and is working with advisers to look at a potential deal between the two. That news sent shares of Charter skyrocketing and analysts speculating on how Verizon would fund a deal of that size. While Verizon would likely have to pay a premium to get a deal done, there are concerns it will take on more debt to bankroll it. Currently Verizon has more than $100 billion in debt, and by adding to that to acquire Charter, there’s fear its credit rating could get downgraded, making the debt riskier. Because of that, the bondholders, in a exchange announced last week, want more protection, reported Reuters. (See also: Charter Stock Surges on Report of Verizon Interest.)

Verizon Exchanging 18 Existing Bonds

Last week, Verizon announced an exchange of 18 existing Verizon bonds for new ones that carry longer maturities. There's also an option to exchange certain bonds for cash. The offer closes Tuesday at the end of business, which Reuters says gives bondholders little time to get the exchanges amended. Bloomberg News, citing people with knowledge of the situation, said investors in the debt exchanges want additional terms added to the new debt they would be swapping into including a step-up coupon if the deal with Charter happens. With it, investors would get a higher interest rate if Verizon’s credit rating is lower after it acquires a company.

While bondholders, investors and analysts are gearing up for a deal between Verizon and Charter, the chances of something actually happening are still at the speculation stage. Shortly after the Journal reported the talks, CNBC cited its own sources as saying that “no significant talks” were taking place. Meanwhile, MoffettNathanson analyst Craig Moffett said in a report that while the deal would make sense, it will be tough to pull off.

For starters, the analyst said there could be regulatory hurdles to a deal getting approved even if the Trump administration is expected to be friendlier to M&A in telecom and cable. What’s more, the analyst said it may be too expensive for Verizon to acquire Charter. “To avoid taking on an unsustainable debt load, a transaction would therefore have to be relatively heavily-skewed toward equity,” Moffett wrote. “Depending on the premium paid, and the mix of cash and stock in the transaction, the leverage of the combined entity could otherwise become unsustainable.” Moffett estimates Verizon would have to pay a nice premium to acquire Charter offering between $400 a share to $550 a share to get it done.