conditionally-hide-shipping-method.php

<?php

/*
 * Conditionally hide shipping methid, based
 * on shipping class found in the cart
 */
function is_shipping_class_in_cart( $shipping_class ) {

    $is_shipping_class_in_cart = false;

	// loop through all items in the cart
    foreach ( WC()->cart->get_cart() as $cart_item_key => $values ) {

        $product = $values['data'];
        $terms = get_the_terms( $product->id, 'product_shipping_class' );

        if ( $terms ) {
            foreach ( $terms as $term ) {
				// check if items shipping class matches $shipping_class
                $product_shipping_class = $term->slug;
                if ( $shipping_class === $product_shipping_class ) {
                    $is_shipping_class_in_cart = true;
                }
            }
        }
    }

    return $is_shipping_class_in_cart;

}

add_filter( 'woocommerce_package_rates', 'conditionally_unset_a_shipping_method', 10, 2 );

function conditionally_unset_a_shipping_method( $rates, $package ) {

	// Use the method id of shipping gateway to conditionally hide. You can find the method id
	// under WooCommerce > Settings > Shipping > Shipping Methods under the ID column.
 	$method_id_to_unset = 'usps';
	// use the slug of shipping class to check for in the cart.
 	$shipping_class_to_detect = 'no-usps';

  	if ( is_shipping_class_in_cart( $shipping_class_to_detect ) ) {
		foreach ( $rates as $rate ) {
			if ( $rate->method_id == $method_id_to_unset ) {
  				unset( $rates[$rate->id] );
			}
		}
	}

	return $rates;

}