BRUSSELS (Reuters) - Axel Springer's SPRGn.DE price-comparison shopping service Idealo and 40 other European peers have accused Alphabet Inc's Google GOOGL.O of tilting the playing field in its favor and urged EU antitrust regulators to enforce a ruling against the company.

The joint call by the group ratchets up pressure on European Competition Commissioner Margrethe Vestager to take further action against Google, the world’s most popular internet search engine, two years after she ordered it to stop favoring its own price comparison shopping service (CSS).

The companies, the largest group to take a stand against Google to date, in a joint letter to Vestager seen by Reuters on Thursday said that the U.S. web giant had yet to comply with the 2017 order. Google was also fined 2.4 billion euros ($2.65 billion) at the time.

The signatories to the letter are from 21 EU countries and include Idealo, Europe’s second largest price comparison shopping service, Polish No. 1 Ceneo, Britain’s Kelkoo, and Foundem and Heureka in the Czech Republic.

“We are approaching you (Vestager) because companies like ours are endangered by Google, which is artfully avoiding compliance with the law,” the companies wrote.

They said Google’s proposal to allow competitors to bid for advertising space at the top of a search page had not boosted traffic to their sites.

“As a result, more and more CSS’ have been or will be forced by Google to exit the market.”

Google said it was seeing positive results from its “shopping remedies” and more merchants were gaining traffic.

“Over 28,000 merchants in Europe are currently placing shopping ads through these third-party Comparison Shopping Services, leading to more choice for merchants and consumers,” Google said.

The European Commission confirmed receipt of the letter, which did not mention any specific solutions sought by the group, and said it was monitoring the situation.

Some 600 companies now take part in auctions for search page advertising space, Google senior executive Oliver Bethell told an Informa conference earlier this week, saying it proved the auctions had boosted competition.

Thomas Hoppner, a lawyer for Idealo said most of the signatories were voicing their frustrations for the first time.

“The letter demonstrates a united front of genuine comparison shopping services against Google’s attempt to present measures as a “compliance mechanism”,” he said.

Earlier this month, Vestager voiced concerns about the lack of significant traffic to Google’s competitors, rowing back on previous comments about the positive impact of the auctions.