Women are effectively working for free from tomorrow until the end of the year.
Men are on average paid 14% more than women.
Dress for Success Dublin has launched its annual #WorkEqual campaign to draw attention to the gender pay gap.
They have designated tomorrow as a day of action during which a range of activities have been planned including an event at Dublin's Liquor Rooms, briefings at Leinster House and an online awareness campaign encouraging members of the public to show their support for ending the gender pay gap.
"This is the third year we’ve run our #WorkEqual campaign, which aims to highlight the gender pay gap, the issues that feed into it, and the measures that can be taken to achieve true workplace equality," said founder Sonya Lennon.
"As the campaign has grown in impact, we’ve noticed more high-profile gender pay gap ‘deniers’ airing their views.
"In recent weeks alone, national media outlets have given airtime and column inches to people who refuse to accept the pay gap exists or who want to paint it as some sort of ‘motherhood penalty’.
"This is ridiculous: impartial statistics agencies – ranging from the CSO to Eurostat – have collated and analysed the data that irrefutably shows Ireland has a gender pay gap of 14%.
Ms Lennon said that those who deny the gender pay gap are "doing a huge disservice to both men and women".
Tomorrow, Senator Lorraine Clifford-Lee will host Dress for Success Dublin to deliver briefings to members of the Oireachtas.
"It is only a matter of time before workplaces in Ireland will be legally obliged to disclose their gender pay gap," said Senator Clifford-Lee.
"Those who deny this issue now are burying their heads in the sand. Instead, they should look to jurisdictions like Australia and the UK to see the positive legislative measures that have been implemented there, and the way in which workplaces have proactively responded."
Dress for Success has also announced the establishment of a ‘Pay Disclosure Pioneers’ initiative, which will see the charity bringing together leading businesses that have committed to early pay disclosure and progress towards workplace equality before Ireland’s proposed new gender pay gap laws come into effect.