The gender pay gap has been highlighted by numerous high profile BBC presenters today, including Mishal Husain and Jo Whiley, who have been photographed wearing t-shirts and holding signs featuring the equals symbol.
"With the state pension slipping further from reach it is vital that auto enrolment works equally for both women and men and removing the auto enrolment trigger and earnings bands is imperative to ensure that this discrimination does not become embedded in our pension system".
The society says the pay of younger women in particular is falling behind that of men, claiming the drive to equalise pay is going backwards and will now take 100 years to close.
SNP Leader Nicola Sturgeon said "My #PayGapPledge is to do everything I can as Scottish First Minister to advance equal pay & gender equality #EqualPayDay'".
'Equal pay is both a cause and effect of gender inequality and it creates the context for other inequalities, such as violence against women and girls and unequal access to health, ' the WEP adds.
The group said the gap was wider than the average for women working full time in their 50s, at 18.6 per cent, but it has also grown among women in their 20s, from 1.1 per cent in 2011 to 5.5 per cent this year.
The Fawcett Society, which campaigns for women's rights, issued the warning as it dubbed Friday Equal Pay Day - saying it marked the time in the calendar year when women start to work for free due to their pay lag on male earnings. The gender pay gap now stands at 14.1%, that's the same as it was in 2015 and 2016.
In the North East it's growing, up from 8.7% to 10.2%.
"We need to change the way in way in which we're tackling the gender pay gap and that sort of wage survey and transparency is a better model".
The gap now stands at 14.1 per cent, the same as it has been for the past two years, and at this rate could take until 2117 to close.
Where Is This "Pay Gap"?I'm pleased that some of our top companies are leading the way and have already reported.
We also need to ask our employers what they are doing to measure and report their gender pay gaps, and what action plan they are putting in place.
Correct - If there are pay discrepancies that can not be objectively justified, then they must be corrected and the causes addressed to avoid a gap reopening.
The Government need to do much more to foster a flexible working culture in our workplaces - the default model needs to be all jobs are flexible working jobs unless there is a good business reason for them not to be.
Breaking down the pay gap between extremely high male and female earners provides us with interesting, and mixed, information.
The Fawcett Society also suggest mandatory gender pay reporting for larger employers, equal parental leave, and encuraging businesses to audit the nature as well as the pay of their work, to "make sure men and women are paid equal pay for work of equal value".