It protests the attacks on humanists, atheists, and secularists, including the brutal murders of five bloggers in the past two year - four of them since February this year. Note that the government of Bangladesh is deeply complicit in the culture of violent suppression of humanist/atheist/secular thought. For example, as stated in the letter:
Furthermore, your Cabinet Committee for Law and Order, headed by Minister of Industries Amir Hossain Amu, on their 9 August 2015 meeting decided “to declare Atheist authors as criminals”, thereby making them subject to prosecution, and intelligence agencies have been asked to monitor blogs to find those atheist writers. Even under the current law, such a mass arrest of people who profess non-religious views in their online communications would represent a grave violation of the international human rights obligations to which Bangladesh is committed. The Home Minister in a separate speech was seen repeating the same warning message.The letter concludes by imploring the Prime Minister and President to take decisive steps to ensure the safety of individuals whose lives are threatened by religious extremists, and to ensure Bangladesh's compliance with international norms relating to freedom of conscience and expression.
Please check out the full text, which contains much detail about the present deplorable situation in Bangladesh.