Charter, which was rebuffed in its bid for Time Warner Cable, said in a statement filed with the U.S. Securities and Exchange Commission that the planned merger of Time Warner Cable and Comcast posed a high degree of regulatory risk and warned that approval could drag on until the first quarter of 2015.

TWC and Comcast announced their all-stock agreement on February 13, which at the time gave the deal a value of $158.82 per share. Charter argued in the filing that, due to Comcast's declining share price, the value was now worth $141.16 a share.

It called the merger process flawed as "the TWC board specifically demanded of Charter $160 per share, and publicly stated that they would not take a penny less than $160 and that the collar was a critical element."

In a response to the filing, TWC said: "We are fully committed to our merger with Comcast, which we believe is in the best interests of shareholders."

(Reporting By Nicola Leske; Editing by Jonathan Oatis)