The gender pay gap for full-time workers has fallen slightly to 9.4%, the lowest for almost 20 years, but remains at around 20% for high earners, official figures show.
The headline figure - the difference between men's and women's full-time median hourly pay excluding overtime - fell from a revised 9.6% in 2015, said the Office for National Statistics. (ONS).
This is the lowest it has been since current records began in 1997, when the gap was 17.4%, although the gap has narrowed relatively little in recent years, said the ONS.
TUC general secretary Frances O'Grady said: "The full-time gender pay gap is closing at a snail's pace. At this rate, it will take decades for women to get paid the same as men.
"We need a labour market that works better for women. This means helping mums get back into well-paid jobs after they have kids, and encouraging dads to take on more caring responsibilities.
"The Government should also scrap tribunal fees, which stop women getting justice from bad employers who have discriminated against them."
The ONS said the introduction of the national living wage of £7.20 an hour for adults had led to pay growth in the past year being at the bottom end of the earnings scale.
ONS statistician James Scruton said there was a definite pay boost for those previously paid below the rate, adding that there was a similar pattern when the national minimum wage came into force in 1999.
The figures, for April this year, showed that weekly earnings grew by 2.2% for full-time workers and 6.6% for part-timers.
The TUC said the figures revealed that 362,000 people were paid below the minimum wage in 2016 - a 73% increase from the previous year.
Ms O'Grady said: "These figures are very worrying. The Government must use next month's Autumn Statement to beef up minimum wage enforcement.
"There should be no hiding place for bosses who try to cheat their workers out of a fair day's pay. Failing to pay the minimum wage squeezes those who have the least."
Business Minister Margot James said: "The Government is determined to build an economy that works for all and it's encouraging that earnings have grown over the last year, with the national living wage driving up the wages of the lowest paid.
"I am particularly pleased the gender pay gap is closing but there is still more to be done to make sure women are treated equally."