TOKYO -- A group of Takeda Pharmaceutical stakeholders including retired managers skeptical about its pending $62 billion purchase of Irish drug developer Shire sent the Japanese company's president an open letter requesting more transparency on the megadeal.

The letter to President Christophe Weber, whose contents were revealed Wednesday, amounted to a questionnaire probing Japan's largest drugmaker for a more detailed explanation of its plans to pay back the debt that will finance the acquisition. The shareholders also asked Takeda to further justify the 65% premium for Shire, publicize minutes of board meetings along with statements by executives, and address other acquisition targets.

Takeda is not legally obligated to comply with the demands, but it confirmed receiving the letter, which gave it an Oct. 31 deadline to respond.

The group of roughly 130 shareholders, calling themselves "Thinking about Takeda's Bright Future," comprises Takeda alumni as well as other individual investors. The coalition owns around 1% of the company, based on voting rights.

During June's regular shareholders meeting, the group submitted a proposal that would require any acquisition exceeding 1 trillion yen ($8.78 billion) to be approved by shareholders. But the motion received less than 10% support.

Takeda announced in May it had reached an agreement to buy Shire, a company with a larger market value. To cover the purchase price, the Japanese company is borrowing 3 trillion yen and issuing roughly 4 trillion yen in new shares. The fundraising needs the approval of shareholders at an extraordinary meeting that is scheduled to take place by Jan. 18.