WC disable sale on all products.

woocommerce-store-wide-disable-sales.php

<?php

/**
 * Disable all sales.
 *
 * A simple function to disable all the sales in the shop.
 * Uncomment the line of code to disable the sale price on products.
 */
function custom_wc_get_sale_price( $sale_price, $product ) {

// 	return $product->get_regular_price(); // Un-comment this to disable all sale prices

	return $sale_price;

}
add_filter( 'woocommerce_product_get_sale_price', 'custom_wc_get_sale_price', 50, 2 );
add_filter( 'woocommerce_product_get_price', 'custom_wc_get_sale_price', 50, 2 );

// add_filter( 'woocommerce_get_sale_price', 'custom_wc_get_sale_price', 50, 2 ); // WC < 3.1.2
// add_filter( 'woocommerce_get_price', 'custom_wc_get_sale_price', 50, 2 ); // WC < 3.1.2