Dozens of H&M shop workers on Tuesday protested outside one of the Swedish fast fashion giant's stores in central Madrid to demand higher pay and lighter workloads, forcing the store to close for a few hours.

Around 4,000 shop assistants also plan to go on strike, called by the two largest Spanish trade unions CCOO and UGT, on June 22 and June 26, just as the summer sale season is set to kick off.

The workers said they decided to go on strike after failing to reach a wage agreement with management after months of negotiations, with the latest meeting lasting 12 hours on Monday. They claimed H&M paid less than its major competitors, including main rival Inditex-owned Zara.

"H&M workers in Spain earn less than 1,000 euros a month," said Santiago Sanza, a 42-year-old shop worker who took part in the Madrid protest. He added most of the staff worked part-time, about 24 hours a week, so they received lower salaries.

"We need to increase wages substantially," Sanza said.

The shop workers in Madrid also complained of excessive work hours in stores, saying employees were forced to cover for colleagues on medical leave without any additional support.

Protesters carried signs reading "No more discount salaries" and "The work it takes three workers to do is being done by one."

H&M declined to comment on the workers' demands but said it "respects the rights of employees to express themselves freely."

Earlier this year, Inditex agreed to a 20% rise in average wages for shop workers in its home market of Spain in response to workers' demands for higher pay to offset soaring consumer prices.

"The increase in Inditex has pushed us to look for better salaries," said shop assistant Ainara Cortez, 38, who has been working at H&M for 16 years. "We know that we cannot fully compare with them, as Zara sell more," she added.

Spain accounts for 3.7% of H&M's global 106,000 shop workforce, 75% of whom are women, according to its annual report for 2022. The fashion brand has more than 10,000 store employees each in its main market, the United States, and its home country Sweden.