Northern Ireland spokesman Baroness Randerson has repeated a statement on Belfast violence, on 11 December 2012.
The statement - made earlier in the Commons by Northern Ireland Secretary Theresa Villiers - followed a petrol bomb attack on a police car outside the offices of Naomi Long, the Alliance Party MP for East Belfast, on Monday.
Trouble has flared across Belfast in the past week, with 29 police officers injured and 38 people arrested.
Loyalist protests broke out following a decision by Belfast City Council to fly the union flag at City Hall on designated days, not daily.
Ms Villiers told the Commons there "can be absolutely no excuse or justification for this kind of thuggish and lawless behaviour".
She said those engaged in violence were "dishonouring and shaming the flag of our country ... and discrediting the cause they claim to support".
Labour said the Commons must send a "clear and strong message" that the violence is "wrong, unacceptable and without justification".