[Plugin: MailChimp List Subscribe Form] Prevent CSS styles from loading

How can I prevent CSS styles from loading? I dont want to have 2 additional CSS calls in head:

mailchimpSF_main_css
mailchimpSF_ie_css

This should work but for some reason mailchimp CSS files are still loaded:

add_action('wp_print_styles','my_deregister_styles', 100);

function my_deregister_styles() {
	wp_deregister_style('wp-mailchimpSF_main_css');
	wp_deregister_style('wp-mailchimpSF_ie_css');
}