A watchdog has launched an investigation into whether children face “unfair pressure” to spend money on apparently free web and app-based games, it said Friday.

The Office of Fair Trading (OFT) is asking parents to get in touch with any examples of possible “commercially aggressive” practices which encourage children to buy virtual currency like coins, gems or fruit, or upgraded membership.

It is unlawful to make a “direct exhortation” to children to make a purchase or persuade their parents to do so under consumer protection regulations.

“We are concerned that children and their parents could be subject to unfair pressure to purchase when they are playing games they thought were free, but which can actually run up substantial costs,” said Cavendish Elthorne, the OFT’s senior director for goods and consumer.