Bondholders are concerned that Verizon’s (VZ) credit rating could be downgraded if it issues new debt in order to acquire Charter (CHTR), making the new bonds riskier, buyside sources told IFR on Friday.

On Wednesday, investors were offered the chance to exchange up to 18 existing Verizon bonds for new bonds with longer maturities. It may also exchange some bonds for cash.

“People would be taking their maturities longer with this trade and a large acquisition would add uncertainty to the picture,” said one investor looking at the exchange. “We are always subject to the possibility of big acquisitions, but the proximity of it is kind of unique here.”

The exchange offer closes at 5 p.m. New York time on Tuesday, giving bondholders a short window to push for better terms to account for the potential changes to Verizon’s balance sheet.

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The Wall Street Journal reported Thursday that Verizon, which has a market cap of $194 billion, was exploring a possible transaction with Charter, which is worth $80 billion.

Verizon has over $100 billion in outstanding debt. In its Q4 earnings report this week, the company reaffirmed its goal of single-A ratings by 2018-2019. It is currently rated BBB+ by S&P, Baa1 by Moody’s, and A- by Fitch.

Coupon step-ups would be the best solution to guard against the risk of Verizon’s credit rating being downgraded because of the acquisition, the investors said.

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“We are talking to the dealer and the company and seeking to have step-up language inserted,” said a second investor.

The company could also offer higher premiums in the exchange or extend the deadline for participation, said a third investor.

Lead dealer managers on the exchange are Citigroup (C), Credit Suisse, Goldman Sachs (GS), Santander, and Wells Fargo (WFC).

Verizon declined to comment.