Spain plans to impose stricter rules on production of a staple of the national diet and increasingly popular export — ham from free-range pigs that feed on acorns and herbs — in order to weed out stable-bound impostors, a newspaper said Sunday.

The salt-cured ham, like Italian prosciutto but darker and chewier, is produced around Spain from a breed called the Iberian pig, a dark, long-legged creature with a pointy snout.

But because of ambiguous laws, the techniques used in many provinces do not comply with traditional standards for the ham to receive a certificate of quality, much like the 'denomination of origin' used in the wine industry, El Pais said.

Now the agriculture ministry plans reforms so that the title 'jamon iberico,' or Iberian ham, will go only to meat from Iberian pigs that graze in open countryside on acorns and herbs like rosemary and thyme — the traditional technique — and not to ham from stabled pigs that are fed grain, as often happens now, El Pais said.

Ham is very serious business in Spain. The industry produces around 5 million legs of salt-cured ham a year, and prized Iberian pieces can retail for more than $260.

Despite that high cost, the ham is a regular on dinner tables and in bars and restaurants serving 'tapas' finger foods.

The United States agreed in 2005 to start allowing imports of the hams after Spanish slaughterhouses upgraded their facilities to comply with U.S. standards, but the curing process takes 23 months so no imports are expected until late 2007.