The rail unions have been in the news lately - for threatening strikes, for one thing, and for another because the government wants to reform the railways and bring in new working practices. In stories about labour disputes and trade unions (such as this one) the term 'Spanish practices' is often used. It refers to irregular working practices that have been negotiated by the unions at some point in the past (examples here).
Although 'Spanish practices' is not a politically correct term and upsets many Spaniards, no slur is intended on the Spanish or their ways of working. It is a phrase used to criticise British workers. It is a very old expression in English and dates back to the rivalry between the Spanish and the English in the 16th century.
'Spanish practices' is not in the OED as a headword or a section in itself, but it is in a citation under 'Spanish'. The 1584 (a few years before the Spanish Armada) citation is: "The French king‥will mislike, that, by any Spanish practice, she should be drawn to violate her faith". The OED says that Spanish here means 'deceitful, perfidious or treacherous'.
A synonym of 'Spanish practices' is 'an old Spanish custom' although this is rarely used these days. That expression dates back less than a hundred years, and the OED defines it as a jocular phrase used when justifying a long-standing practice which is unauthorised or otherwise irregular.
Given the centuries-old history of wars and rivalry between England and Spain, insults or negative words have occasionally made reference to Spain or the Spanish. Spanish pox or Spanish gout was syphilis in the 16th/17th centuries and Francis Grose, in his Dictionary of the Vulgar Tongue, has Spanish padlock being a chastity belt, and Spanish trumpeter being a braying ass. The English didn't single out the Spanish when it came to pejorative words. French compliment, French disease, French evil, French goods, French measles and French marbles have all been used as synonyms for syphilis and a French crown was the baldness associated with syphilis - Shakespeare uses it in A Midsummer Night's Dream. A French synonym for syphilis, incidentally, is la maladie anglaise, or the English disease, and I remember that when I studied in Russia in the 1970s they used the term 'English flu' for syphilis. No matter where you are in the world, foreigners get the blame for the evils in society!