People across Ireland are being urged to pledge their allegiance to the republic as declared in 1916 - on the same day as the coronation of King Charles in London.
The pledge is also expected to be taken by those attending an anti-monarchy rally on the Tyrone/Donegal border on Saturday.
The British monarch is expected to be crowned during a lavish ceremony at Westminster Abbey attended by international leaders and royals from across the globe.
The event will include the Homage of the People, during which royalists will be invited to swear an oath of allegiance to King Charles.
The 1916 Societies, which is an all-Ireland group, is planning to hold a rally on Lifford Bridge, which links Strabane in Co Tyrone and Lifford in Co Donegal, to coincide with the coronation.
The organisation is urging people across Ireland to reaffirm their commitment to the republic declared during the Easter Rising.
The vow people are being asked to make on Saturday reads: "I pledge allegiance to the Irish republic as declared in 1916".
Mid Ulster independent councillor Barry Monteith said that "as Irish republicans it is only right we pledge our allegiance to the republic as declared in 1916".
"We state this is opposition to monarchism in all its forms," he said.
"We are opposed to inherited power and privilege. Everyone is born equal."
Mr Monteith said the message coming from Saturday's rally will be "that we reject the British crown territorial claim over Ireland".
"We reject the crown which put medals on the chests of those who have killed, starved and exiled generations of Irish people," he said.
Tyrone trade union activist Brian Forbes is expected to speak at the rally.
"Monarchy is immoral and a scandalous waste of money," he said.
"It is an antiquated system of oppression which perpetuates class divisions.
"Royalty is incompatible with the republican principles of equality and democracy."
The anti-monarch rally will take place at Lifford Bridge at noon on Saturday.
