(Bloomberg) -- Abcam Plc founder Jonathan Milner is threatening to resume a boardroom battle at the biotechnology supplier he started 25 years ago, weeks after the company said it would explore a sale.

Milner, who owns about 6.1% of Abcam, has been agitating for change at the company, asking to be named executive chairman alongside the removal of three directors. Milner argued in an open letter to shareholders on May 30 that Abcam’s incumbents lacked a “shareholder mindset” — and urged them to seek a buyer. 

Milner paused his campaign in June after the company said it would explore “all options” including a potential sale of the company after receiving inquiries from “multiple parties.”

Read More: Life Sciences Firm Abcam Gets Approaches While Battling Founder

However, in an open letter due to be sent to the Abcam board on Wednesday, and reviewed by Bloomberg News, Milner said he was “disappointed” that his offer to rejoin the board hadn’t been acted upon. Since then, he said he had been provided with “one unsatisfactory call” with management. 

“Should you continue to refuse my offer, and continue to under-deliver, I will call the board accountable again and will resume my campaign in the autumn,” Milner said in his letter. He’s given the board a deadline of Aug. 31 to provide an update, when Abcam is due to report interim results. “I have been contacted by many shareholders who are similarly supportive of a sale of the company at a full and fair value.”

A spokesperson for Abcam responded by pointing to the company’s statement on June 23, in which it said it didn’t intend to comment further on its strategic review. It said in that statement it would “make further announcements in accordance with its ongoing disclosure obligations and pursuant to applicable laws and regulations.”

Abcam first listed on London’s junior market, Aim, and has been trading on the Nasdaq since 2020, dropping its UK listing last year. It runs an online store selling protein research tools to scientists and has been called the “Amazon of antibodies.” 

Milner, 58, started the company in 1998 and remained chief executive officer until 2014. He then became deputy chairman, before stepping down from the board in October 2020.

Bloomberg reported in June that Abcam had attracted initial interest from US life sciences companies Danaher Corp. and Agilent Technologies Inc.

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