They are due to appear in Hastings District Court on Monday. Hastings-Havelock North ward councillor Damon Harvey said it wasn't the first time a council facility had faced gang conflict - a similar attack took place at the Havelock North public pools in December.
"A library should be one of the safest public places that people can visit. It's time we start discussing a patch ban in the CBD and in public facilities such as libraries."
Hastings mayor Sandra Hazlehurst said the "latest increase in gang activity is not acceptable in our community".
"Government legislation is very clear (since 2013) that gang insignia is prohibited on government and local government (council) premises."
Hastings District Council community facilities spokeswoman Dennise Elers said the Hastings Library did not proactively enforce the Prohibition of Gang Insignia in Government Premises Act of 2013.
Hazelhurst says in the wake of the attack she has reinforced the importance of police enforcing this law.
"I will be stressing to our staff the importance of phoning the police every time gang insignia or colours are seen at our facilities.
"Our priority is always the safety of our community and therefore our kaitiaki must sometimes make a judgment call before asking a person to leave," she said.
"Our council works very hard to ensure Hastings is a great place to live, work and play. Therefore we have zero tolerance for behaviour that puts at risk the safety of our community."
Harvey said the "cup of tea meeting" which Hazlehurst had with leaders of Mob last week after a patching ceremony on Te Mata Peak was "obviously not a strong enough step".
But the mayor says the two Hastings chapter leaders she met with were "very supportive of doing better".
Figures released to Hawke's Bay Today for the seven-month period from August 2018 to the end of February this year show there were 1951 problematic incidents reported by staff across the district's three libraries.
These range from abuse to people bringing dogs inside.
Of the 197,973 people who entered the Hastings Library, 688 incidents were reported.
For Havelock North Library, 68,131 people came through the doors, and 85 incidents were reported. Of the 71,220 visited Flaxmere Library, 1178 incidents were reported.