A German private-sector competition watchdog has filed for an injunction against online fashion retailer Zalando, it said on Thursday, accusing the group of false advertising.

The Centre for Protection against Unfair Competition said in a statement that Zalando had in its online shop misrepresented how many pieces of certain items of clothing were still available, creating the impression that customers needed to act fast to buy them.

It said it filed the suit with a regional court in Berlin.

Zalando shares were down 2.2 percent, compared with a flat German mid-cap index.

Zalando said in a statement that it had already reacted after the watchdog raised concerns a few months ago, changing wording on its website.

"We are very surprised that the next step is the filing of an injunction," it said.

Zalando said the site was accurate when it said there were only one or two items available of a particular garment. However, when it said "three items available", more than three could be in its warehouse, so it has changed the wording to be more precise to either "three items available " or "more than three".

Most German trade corporations are members of the Centre for Protection against Unfair Competition, a self-regulatory body, which regularly initiates legal action against groups which infringe laws concerning unfair competition.