The terms Spanish practices or old Spanish customs are United Kingdom expressions that refer to irregular or restrictive practices in workers' interests. Typically, these are arrangements that have been negotiated in the past between employers and unions.
Brewer's Twentieth Century Phrase and Fable describes the phrase (rather unconvincingly) as 'industrial slang for restrictive practices, so called because of the punitive treatment meted out by the Spanish Inquisition'. Nigel Rees, in his Phrases and Sayings, says it's not clear why the Spanish are blamed, 'except that Spaniards tend to attract pejoratives - not least with regard to working practices (the maņana attitude)'. A glance at Partridge's Dictionary of Slang shows that the British have taken delight in abusing the Spanish for centuries: 'Spanish gout' was syphilis; 'Spanish padlock' a chastity belt; a 'Spanish trumpeter' an ass braying (as in Don Key).
Which ever way you look at it the terms and conditions in Iberia for new joiners are going to be less generous. Those present employees are going to have to adjust their expectations or learn basic Mandarin.