stranglehold
noun [ C, usually singular ]
disapproving uk/ˈstræŋɡlhəʊld/ uscomplete control over a market, an industry, etc. that does not allow fair competition from other businesses:
break/loosen/tighten a stranglehold The Association campaigned for America to break the stranglehold of foreign oil.
have a stranglehold on/over sth The banks still have a stranglehold on the credit card market, despite many new providers offering lower interest rates.