Simple Form Blank Label
Have you tried label:false instead of label:"":
<%= f.input :email, class: "login-field", label: false %>
Old question but it worked for me, @Josh M:
<%= f.input :email, class: "login-field", label: ' '.html_safe %>simple_form (3.0.2)
I think the way to go is label: false
Also in simple_form_for you may pass defaults: {label: false} to disable label for all fields in this form.