A protest last Saturday in Belfast saw members of the fringe Republican group Eirígí load up shopping trolleys with Israeli goods and exit the store.
While in Dublin on Thursday evening protesters abandoned full shopping trolleys at checkouts while handing out letters calling for a boycott of the store due to its supposed support of Israel.
Both incidents involved dozens of protesters and brought store operations to a halt.
A spokeswoman for the store& said: “We will, if we need to, take appropriate security measures to protect employees, customers, products and property.”
She added: “This is part of wider boycott campaign of Israeli goods. We are particularly targeted because there is a rumour that we are supportive and provide profits to Israel. This is completely unfounded.”
Eirígí has stated it intends to carry out further protests. A spokesman said: “We are calling on people to boycott Marks & Spencer until it stops stocking Israeli goods and cut its links with what is nothing short of a rogue state.”