Basic pay in the UK economy grew by just 1.7% year-on-year in the three months to April.
The figures, released by the Office for National Statistics, are worse than expected, and represent the lowest rise in regular pay since February 2016.
If bonuses are included, average pay grew by 2.1% - still not enough to keep pace with inflation, which was 2.7% in April, and 2.9% in May.
The ONS says latest estimates show that average weekly earnings for employees in Great Britain in real terms (that is, adjusted for price inflation) fell by 0.4% including bonuses, and fell by 0.6% excluding bonuses, compared with a year earlier.
TUC general secretary Frances O’Grady said: “Real wages have fallen for the second month in a row. Unless the government gets its act together, we’ll soon be in the middle of another cost of living crisis.
“Ministers must focus on delivering better-paid jobs across the UK. And it’s time to bin the artificial pay restrictions on nurses, midwives and other public sector workers.
“Britain needs a pay rise, not more pressure on household budgets.”