North American vinyl building products company Axiall has unanimously rejected a second bid from rival Westlake Chemical, this time worth $3.1 billion. Westlake has subsequently responded by formally ending negotiations and asking Axiall’s shareholders to elect a new board.

The revised bid, submitted on Mar. 29, offered $23.12 per Axiall share. This was an increase on the $20 per share offered in January this year, which valued Axiall at $2.9 billion.

In a written response, Axiall CEO, Timothy Mann described the offer as “inadequate”. He said the value proposed by Westlake ignores the high quality of Axiall’s assets, its significant growth potential and the powerful synergies available in a combination, adding that the new bid is inconsistent with the board’s understanding from a meeting held in Houston on Mar. 8.

Mann said he believes the synergies from a merger could be as high as $270 million annually, some $210 million more than the $60 million in synergies outlined in Westlake’s proposal.

In his letter to Axiall shareholders, Westlake CEO Albert Chao said the company would now file preliminary proxy materials with the US Securities and Exchange Commission (SEC) to elect 10 new candidates for the rival’s board, who would be “willing to evaluate all options in accordance with their fiduciary duties.”

Chao said Axiall’s board had refused to make a counterproposal or otherwise negotiate or provide any constructive feedback. He added that the company had consistently overestimated its earnings power and had a track record of failing to deliver on its operational and strategic objectives.

Axiall, formerly known as Georgia Gulf, has been under pressure in recent weeks from its biggest investor, Shapiro Capital Management, to negotiate with Westlake.