Special interest groups with much money can hire lobbyists to influence politicians. An example is if special interest groups lobby for tariffs in order to protect their home market from foreign competition. This will increase prices in the home market, and thus rents are obtained by the special interest groups.
The classical example are the english corn laws in the 19th century, but the wish for protection seems hard to resist, also by many who pretend to be champions of free markets.
Rents 