You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Political_party

Context:
Furthermore, in the case of far-right, far-left and regionalism parties in the national parliaments of much of the European Union, mainstream political parties may form an informal cordon sanitarian which applies a policy of non-cooperation towards those "Outsider Parties" present in the legislature which are viewed as 'anti-system' or otherwise unacceptable for government. Cordon Sanitarian, however, have been increasingly abandoned over the past two decades in multi-party democracies as the pressure to construct broad coalitions in order to win elections – along with the increased willingness of outsider parties themselves to participate in government – has led to many such parties entering electoral and government coalitions.

Question:
which  outsider parties considered unacceptable to work with?

far-right, far-left and regionalism