(Bloomberg) -- Teck Resources Ltd. has suffered a blow to its plans to separate its coal and metals operations after a major advisory firm urged shareholders to reject the move, complicating its fight to thwart a $23 billion takeover from Glencore Plc.

The battle is heating up just as the top executives of Teck and Glencore converged on Toronto in an attempt to shore up shareholder support for their companies’ own competing visions of the future of the Canadian miner.

In the past four days, Teck has been forced onto its back foot on defending its future. The latest setback came as Institutional Shareholder Services Inc. recommended investors vote against Teck’s separation, citing “uncertainties and structural issues associated with the proposal.” The company had made a concession to accelerate its coal split to win over investors earlier Thursday, days after ramping up its rhetoric against Glencore’s bid and its management.

“Between the ISS recommendation and a higher Glencore bid likely coming, the vote really seems to be in jeopardy,” Canaccord Genuity analyst Dalton Baretto said in an interview. “I would not be surprised to see management tweak the proposal.”

Teck Chief Executive Officer Jonathan Price and Glencore CEO Gary Nagle are making the rounds in the global mining capital, lining up competing meetings with top Teck shareholders while escalating the war of words between the rivals. Glencore’s CEO aims to use a Thursday luncheon to sway investors on its takeover proposal.

Shares of Vancouver-based Teck rose 1.8% to C$58.86 at 12:09 p.m. on the Toronto Stock Exchange, one of the world’s biggest bourses for mining companies.

Price reinforced his firm’s stand on Glencore’s latest revised offer, calling it “another non-starter” in interviews. He framed the accelerated separation of the coal business “optimal” for investors since it will create “an entirely standalone, self-funded world-class copper business.”

ISS said the separation appears “less compelling” than the company’s status quo or “alternative structures which could be sought,” according to its Thursday report. Shareholders are scheduled to vote on the plan at an April 26 meeting in Vancouver.

The battle over Teck comes as acquisition activity heats up in the mining industry, fueled by demand for more of the metals that underpin the global energy transition. Teck’s assets are appealing to several top mining companies including BHP Ltd. and Rio Tinto Group, which are said to admire the company’s copper mines in the Americas.

Read More: Glencore Tweaked Teck Bid As Some Investors Balked at Coal

Glencore stepped up its pursuit of Teck with a revised proposal Tuesday that offers an $8.2 billion cash component to address investor concerns over exposure to coal assets.

What Bloomberg Intelligence Says:

Teck’s rejection of Glencore’s revised bid, which included an $8.2 billion cash component but no bump in offer premium, puts the ball back in Glencore’s court. Glencore may need to add around $2-$3 billion to its bid, in our view, just to start addressing Teck’s concerns around valuation. Even then, it’s conceivable that Teck’s board will continue to urge shareholders to vote for its own separation plan on April 26, after tweaking the transaction terms to allow for an earlier separation of the unbundled coal and metals companies.

— Alon Olsha, BI metals and mining analyst

--With assistance from Joe Deaux.

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