CORRECTED-Mexico's Calderon slams corporate tax dodgers

(deletes or clarifies references to Slim in 1st, 7th, 8th graphs to make clear Calderon did not mention him by name; corrects name of PRI)

MEXICO CITY, Oct 29 (Reuters) - Mexican President Felipe Calderon, struggling to get tax hikes past Congress, on Thursday scolded big firms for not paying their fair share of taxes.

Calderon needs votes from the opposition Institutional Revolutionary Party (PRI) to raise value added taxes in order to patch a growing fiscal gap due to sliding oil production.

The conservative president has run up against resistance from the centrist PRI and left-wing politicians loathe to back tax increases as the economy slowly emerges from its worst recession in decades.

Opposition parties have demanded he do more to increase revenues from Mexico's biggest companies.

"I am not asking companies in Mexico to pay more than what a dentist, an employee, pays. I am asking them to put in what they need to, to observe the law," a visibly upset Calderon said in a speech delivered to business leaders in Mexico City.

Bond rating agencies have warned Mexico faces a downgrade of its debt unless concrete steps are taken to improve the sustainability of public finances.

"It is ok that they have philanthropic activities, that they sponsor sports and cultural events, that they donate medical equipment, but they need to pay (taxes) too," Calderon said.

All the activities Calderon mentioned were specific to the companies of retail and telecoms tycoon Carlos Slim.

Slim, one of the richest men in the world, is well known for his philanthropic activities and Telmex (TMX.N) (TELMEXL.MX), Mexico's dominant fixed-line telecoms company and the heart of his business empire, frequently sponsors car races, charities and concerts.

Slim's Instituto Carso assists poor families with medical costs and donates equipment to clinics serving less well off Mexicans.

Corporate charitable donations can usually be partially deducted from tax bills in Mexico.

A spokesman for Slim was not immediately available for comment. (Reporting by Cyntia Barrera Diaz)