withholding tax when paying a s.l. company

I have been told that our club when paying rent to the land holding s.l. company must withhold tax.
Is this true?
I support Spanish companies (IT support) and apart from professionals they do not withhold taxes.

Property Rentals in Spain are subject to 18% witholding tax. Exemptions apply if the landlord gives you a letter from the taxman showing stating are exempt.

For further information, please read http://reformafiscal.meh.es/preguntas_retenciones.asp (Spanish).

Regards