The Fawcett Society has challenged Brown to become the first prime minister to ensure women and men in the UK are equally rewarded for their work.
Although equal pay legislation has been in force for more than 30 years, women working full time still earn on average 17% less per hour, official figures show.
The group wants the government to set a date for finally closing the gap. At the current rate of progress, it is estimated it would take up to 80 years for that to happen.
The Fawcett Society said a range of measures should be introduced to help close the gap within 10 to 15 years.
These include mandatory equal pay audits for all companies, a right to work flexibly for all employees, and fully signing up to the Working Time Directive.