* EU regulators concerned by restrictions to Web-based services
* European commissioner determined to protect "net neutrality"
* Web providers say some services cut because of congestion
LYON, France, April 18 (Reuters) - The European commissioner responsible for regulating the Internet warned Web service providers on Thursday against tampering with customers' Internet access based on how much they pay or which services they use.
Some Internet service providers (ISPs) want fast and slow lanes for Web traffic, allowing them to charge more for services which use up more space on the radio frequencies carrying the Internet, such as online television or video chat.
In an effort to preserve what they call "net neutrality", European Union governments have considered enforcing laws preventing providers from offering differentiated tiers of access, but so far only the Netherlands has succeeded.
"I am committed to safeguarding net neutrality," Neelie Kroes, the European telecommunications commissioner, told an Internet conference in Lyon. "Everyone should have the option of full access to a robust, best-efforts Internet."
Evidence from European regulators and Internet activists shows that some Web-based companies such as Skype have been blocked or stalled by mobile Internet operators because they discourage customers from using the phone to make calls.
A draft report compiled by European regulators said that some ISPs "throttle" video streaming. ISPs counter that there are legitimate reasons for doing so, such as Web congestion.
The Dutch government introduced net neutrality regulations in October last year after Dutch carrier KPN said it would charge users more if they wanted to use Skype or WhatsApp, a free mobile texting service.
Internet activists who say they are frustrated by the Commission's slow pace of digital reform have reported 162 cases of blocked or slowed services since 2011 and have called on the EU's executive to take sterner action against ISPs.
"We have strong evidence, including on our reporting platform RespectMyNet.eu, that infractions are widespread," said Jeremie Zimmermann of La Quadrature du Net, an NGO.
The association of international telecommunications users, INTUG, said Internet providers should be more transparent if they need to cut services because they are running out of space.
The group compares Internet congestion to road traffic jams or electrical blackouts, saying that in both cases steps can be taken which are clear to the public, such as speed bumps or fuses which switch off electricity.
"But restricted lanes for certain makes of car would not be tolerated," INTUG said. (Reporting By Claire Davenport; editing by Luke Baker)