Updated 2.35pm
A dead cat stuffed into a brown paper bag was left on Stefan Zrinzo Azzopardi's doorstep, the PL said in a statement on Sunday morning.
The bag had an offensive anti-government message scrawled onto it. The statement did not clarify whether Dr Zrinzo Azzopardi had reported the discovery to police.
In a statement, the PL said it stood by its MP in what it called "a clear act of intimidation" and urged for greater unity.
Dr Zrinzo Azzopardi also called for people to come together, saying that "all this happened on my family's doorstep, but I will not be beating the drums of war."
"This will spur me to work harder for unity," he said, as he echoed the Prime Minister's call for PL supporters to attend the party's annual May 1 rally.
In separate statements, both Speaker Anġlu Farrugia as well as Partit Demokratiku offered Dr Zrinzo Azzopardi their support following the "cowardly" act.
"Such vile acts only undermine social cohesion," PD said, as it urged people to switch off political blinkers "which otherwise lead to barbarity of this kind."