Some have vowed to meet the protesters with “loaded weapons” and block roads around Leinster House.
Pals of gangster Ryan have been contacting associates across the country in advance of the planned protest on Kildare Street.
Detectives are monitoring social networking sites which are being used by IRA thugs to stir up trouble.
Senior gardai met with controversial loyalist and protest organiser Willie Frazer today amid mounting fears of a repeat of the violence which brought chaos to the capital after the Love Ulster parade (far left) in 2006.
Justice Minister Alan Shatter said he hopes people will “not opportunistically try to create trouble” on Saturday.
Mr Shatter has vowed that gardai will be prepared for any potential violence.
The Union flag was raised over Belfast City Hall for the first time today since a council decision not to fly it every day sparked the protests.
The flag is flying to mark the 31st birthday of Kate Middleton.
Gardai are monitoring Facebook and other social networking sites used by republican thugs to build up numbers.
Individuals have threatened to use violence against the loyalists and have discussed breaking up in groups to draw gardai to different locations.
“As long as there is Brits and the likes occupying our country there will always be war against these scum,” says one message on Facebook.
One online post on a page linked to the ‘County Sovereign Movement’ ran: “These dirt bags have some neck, as we know it, to even fly their dirty flag in our native Belfast never mind coming to our city of Dublin to even think there [sic] going near our Tri colour that we have fought tooth and nail for this hundreds of years.
“I wonder what roads they might take? One thing for sure, they won’t get far.”
Minister Shatter said that the 150 protesters expected to travel from the North are “are entitled to protest in peace on our streets in a democratic way”.
He added: “I would hope that other individuals won’t opportunistically try and create trouble should such protests occur. But the gardai are, as I understand it, preparing for any eventuality that might occur.”
Meanwhile, while the loyalists have said they will ask the Government to lower the Tricolour on Leinster House on Saturday, the Oireachtas says that it will already be down.
A spokesman said the Tricolour would not be raised as Saturday is “not a Dail sitting day”.
Willie Frazer, who has received death threats ahead of the protest, was meeting senior gardai in Dublin today.
But there were increasing signs today that there could be violence on the streets on Dublin if the protest goes ahead.
Frazer has said that he could cancel his protest if there is a risk of disturbances.