Spain has this week adopted a SOPA-style law that allows sites to be blocked if they are found to be distributing unauthorised copyright protected material. However, the story behind how the law came to be appears to have more than a little underhand US involvement, according to a report in newspaper El Pais.

As TorrentFreak explains, leaked letters reveal that the US Ambassador to Spain put pressure on the country’s government to push through the legislation, called the Sinde Law, threatening to add Spain to the Special 301 Report Priority Watch list of countries the US thinks is not doing enough to protect intellectual property rightsholders against piracy. Other countries on the list include China, Russia and, perhaps surprisingly, Canada.

Being on this list can lead to trade sanctions being imposed, blocking a country from exporting certain goods to the US if it is deemed to not be taking action the US believes appropriate for protecting copyright holders. With Spain’s economy far from healthy right now, that’s a potentially serious problem.

Although the threat was reportedly made in a letter to the outgoing Spanish government in the last days of its term, the new government was also reportedly warned by the US Ambassador that foreign investment may leave Spain if new intellectual property laws weren’t passed. The new government took office on 21 December, and the Sinde Law was passed on 3 January, just two weeks into its term.

While backroom lobbying isn’t exactly a rare thing when it comes to anti-piracy laws, the leaks reported by El Pais certainly appear to lift the lid on why Spain’s strict new site-blocking came in when it did.