Barclays CEO John Varley will get an earful from Atticus Capital this week, as the firms battle over Barclays’ proposed merger with Dutch bank ABN Amro.

The British bank has reportedly held a number of meetings with Atticus, which owns about 1% of its shares, this month, and Varley will speak to Atticus Vice Chairman David Slager via conference call on Wednesday.

In the Sunday Times yesterday, Slager warned Barclays that if it pursues the bid for “an inferior business in an auction at inflated prices,” the New York-based hedge fund would seek to block the deal.

“We are canvassing shareholders at the moment and we cannot find any that support this deal,” he told the newspaper. “Atticus by itself would not have an impact, but we are confident that shareholders support us in aggregate and the deal will be blocked.” But The Times casts doubt on Atticus’ claims of support, reporting that most large Barclays shareholders are willing to back the bid—as long as the price does not rise.

“We are not against the principle of Barclays expanding into different geographies—for instance we would be supportive of a merger of equals or organic growth in a new market—but we cannot support this deal that destroys shareholder value,” Slager said, making his case. “Our central case is that Barclays should not be using its undervalued paper to buy ABN Amro in a competitive auction.”