written proposal; letter of request; open letter
A formal written document presenting a proposal, request, or opinion, often addressed to an organization or public body. It may be an open letter.
The residents submitted a written proposal to the city requesting the preservation of the park.
The labor union sent a letter of request for a wage increase to the company.
要望書 is a written request or petition, similar to 申し入れ書, but 申し入れ書 often implies a more formal, sometimes public, statement of position or proposal.
Compound of 申し入れ (もうしいれ, 'proposal, statement', from 申し入れる) + 書 (しょ, 'document').