BRUSSELS (Reuters) -EU antitrust regulators, who are examining European satellite company SES's $3.1-billion bid for Intelsat, have asked the two companies' customers whether Elon Musk's Space X-owned Starlink is a credible rival to them.

The responses, due on Monday, will determine whether the European Commission, the EU executive, clears the deal with or without concessions or opens a full-scale investigation if it has serious concerns.

SES operates a multi-orbit fleet of around 70 satellites that provide services, including video broadcasting, government communications and broadband internet.

As the European Union seeks to develop an alternative to the U.S. companies, SES in common with other European satellite companies is seeking greater scale to better compete with Starlink and Amazon's Project Kuiper.

In a questionnaire sent to third parties and seen by Reuters, the EU competition watchdog asked if low-earth orbit satellites, such as those of Starlink and Eutelsat's OneWeb, are credible rivals for the supply of two-way satellite capacity.

They also wanted to know if low-earth orbit suppliers are taking part in tenders and customer contracts and winning them, and how they will affect competition in the next five years.

Respondents were asked whether they have the negotiating and bargaining power to secure favourable terms and conditions when purchasing two-way satellite capacity from SES and Intelsat, and if they can easily switch to a rival supplier.

The Commission has set a June 10 for its preliminary review of the deal.