Disables specific shipping methods if there are products with one or more specified shipping classes in the cart.

wc-disable-shipping-for-classes.php

<?php

/*
Plugin Name: WC Disable Shipping for Classes
Description: Disables specific shipping methods if there are products with one or more specified shipping classes in the cart.
Author: Coen Jacobs
Author URI: http://coenjacobs.me
Version: 1.0
*/

add_filter( 'woocommerce_available_shipping_methods', 'wcdsfc_shipping_method_filter' );

/**
 * Filters the array storing all available shipping methods on checkout
 *
 * Removes some of them if products match specified shipping classes
 *
 * @param array $available_methods Contains the available shipping methods
 */
function wcdsfc_shipping_method_filter( $available_methods ) {
  global $woocommerce;

	// Define the shipping classes that need to cause the disabling of
	// specific shipping methods if in cart. Key is the slug of the
	// shipping class, where the value of the array contains an array
	// with all the shipping methods it needs to disable when one or
	// more products match the key shipping class.
	$check_shipping_classes = array(
		'heavy' => array( 'free_shipping' ),
	);

	if ( ! empty( $woocommerce->cart->cart_contents ) ) {
		// Cart is not empty, now loop through the cart and check for the shipping classes defined above
		foreach ( $woocommerce->cart->cart_contents as $product ) {
			foreach ( array_keys( $check_shipping_classes ) as $shipping_class ) {
				if ( has_term( $shipping_class, 'product_shipping_class', $product['product_id'] ) ) {
					// Loop through the shipping methods that need to be disabled, and do so if they are available now
					foreach ( $check_shipping_classes[ $shipping_class ] as $shipping_method ) {
						if ( isset( $available_methods[ $shipping_method ] ) ) {
							unset( $available_methods[ $shipping_method ] );
						}
					}
				}
			}
		}
	}

	return $available_methods;
}