Google has barred phone maker Huawei off from some updates to the Android operating system, dealing a blow to the Chinese firm.
New Huawei smartphones will also lose access to popular Google apps.
The move comes after the Trump administration added Huawei to a list of companies that American firms cannot trade with unless they have a licence.
In a statement, Google said it was "complying with the order and reviewing the implications".
Huawei declined to comment.
What does this mean for Huawei users?
Huawei will no longer get Google's security updates and technical support, and any new devices will no longer have apps such as YouTube and Maps.
Existing Huawei smartphone users will be able to update apps and push through security fixes, as well as update Google Play services. But if Google releases a new version of Android, Huawei won't be able to offer the update on its phones.
Huawei can still use the version of the Android operating system available through an open source licence.
Ben Wood, from CCS Insight consultancy, said the move by Google would have "big implications for Huawei's consumer business".
What can Huawei do about this?
Last Wednesday the Trump administration added Huawei to its "entity list" which bans the company from acquiring technology from US firms without government approval.
In his first comments since being placed on the list, Huawei chief executive Ren Zhengfei told Japanese media on Saturday: "We have already been preparing for this."
He said the firm, which buys about $67bn (£52.6bn) worth of components each year according to the Nikkei business newspaper, would push ahead with developing its own parts.
Huawei faces growing backlash from Western countries, led by the US, over possible risks posed by using its products in next-generation 5G mobile networks.
Several countries have raised concerns that Huawei gear could be used by China for surveillance, allegations the company has vehemently denied.
Huawei has said its work does not pose any threats and that it is independent from the Chinese government.
Still, some countries have blocked telecoms companies from using Huawei products in 5G mobile networks.
So far the UK has held back from any formal ban.
"Huawei has been working hard on developing its own App Gallery and other software assets in a similar manner to its work on chipset solutions. There is little doubt these efforts are part of its desire to control its own destiny," said Mr Wood.
Short-term damage for Huawei?
In the short term, this could be very damaging for Huawei in the West.
Smartphone shoppers would not want an Android phone that lacked access to Google's Play Store, its virtual assistant or security updates, assuming these are among the services that would be pulled.
In the longer term, though, this might give smartphone vendors in general a reason to seriously consider the need for a viable alternative to Google's operating system, particularly at a time the search giant is trying to push its own Pixel brand at their expense.
As far as Huawei is concerned, it appears to have prepared for the eventuality of being cut off from American know-how.
Its smartphones are already powered by its own proprietary processors, and earlier this year its consumer devices chief told German newspaper Die Welt that "we have prepared our own operating systems - that's our plan B".
Even so, this move could knock its ambition to overtake Samsung and become the bestselling smartphone brand in 2020 seriously off course.