Police officers stood at the door of Auckland's Heritage Hotel last night, as about 80 protesters played music and chanted outside the venue.
Sophie Morgan of Auckland Action Against Poverty (AAAP) said the group was protesting the event to draw attention to increased inequality.
She said beneficiaries, the unemployed, and low-wage workers were hit the hardest, while the rich continued to benefit.
"The Young Nats are celebrating while the policies of the National Party continue to wage a war on the poor."
The group had labelled the protest an 'alternative party', and Morgan said the presence of about 20 police officers seemed excessive.
"The cops showed up before we did, there were at least 20 of them standing outside the doors despite us always saying we were just there to have an alternative party."
No members of the Young Nats came out to engage with the protesters, Morgan said.
Some members of the public watched on, however.
"It went really well, I think we got our message across."
The protest comes just two days after AAAP's three day Mangere Impact sessions came to a close - where volunteers help hundreds of beneficiaries access all welfare assistance to which they are entitled.
This year was their biggest Impact yet, helping about 700 people, some who lined up outside the South Auckland WINZ office from as early as 6.30am.
The group had to turn even more away than they were able to help.
This included families who had travelled from Whangarei for a food grant, as well as mothers with babies who had walked miles to get there, Morgan said.
"AAAP believes that the contrast between the Young Nats' Ball and the lives of the people seen at this year's Impact is disturbing.
"Tonight the Young Nats are paying $128 for a ticket to drink expensive champagne and rub shoulders with current Prime Minister John Key and former Prime Minister Jenny Shipley."