The Campaign for Public Housing began what they call an "occupation of disruption" at Permanent TSB's Grafton Street branch at lunchtime today.
The occupation is a protest against the bank's proposed sale of €4b worth of distressed mortgages to so-called "vulture funds".
A number of councillors are staging the protest, including TD Joan Collins.
"This sale is just the beginning. If it’s allowed to go ahead, Ulster Bank and many others will take it as the starting gun to begin similar, mass sell-offs of any mortgage not making them enough profit," she said.
"Our occupation here today is intended to show the government that, if these loans are not stopped, there will be a fight back."
Campaign spokesperson Cllr. Cieran Perry said:
"The purpose of our Campaign is to ensure that those who are causing the housing crisis - government, banks, estate agents, developers - are not allowed to continue with 'business as usual.' They cannot be allowed to put the lives of almost 20,000 households in jeopardy and not be held to account."
Cllr. Éilis Ryan, Campaign spokesperson said expansion of the housing system is the only solution to the current housing crisis, the group wants for the state to take ownership of all buy-to-let mortgages currently involved in the TSB sell-off, which means the state would "effectively become the landlord of those 7,000 tenants".