The firm blogged that it did this "globally". A spokesman confirmed that this included streams sent via UK mobile operators.
However, some firms - including T-Mobile and Sprint in the US - are not affected by the cap.
Netflix said its intention was to stop its members facing excess charges.
But one of the US's biggest networks has reacted with anger.
"We're outraged to learn that Netflix is apparently throttling video for their AT&T customers without their knowledge or consent," AT&T told the Wall Street Journal.
AT&T and Verizon, another US operator, had been accused of imposing the restrictions themselves as a result of confusion caused by a recent T-Mobile ad campaign.
"Here's a little factoid for you," said T-Mobile's chief executive John Legere in a video posted on 17 March.
"Did you know that when you watch Netflix on T-Mobile you get it at 480p [resolution]?
"The duopoly is actually delivering your Netflix content at 360p. I'll bet you didn't know that. Go check. it's true."
Netflix indicated the discrepancy was due to the fact that T-Mobile and Sprint slowed down  customers' data speeds, rather than charging them more money, when they went over their usage limit.
Netflix's chief executive has previously described himself as being a defender of "strong net neutrality".
"The essence of net neutrality is that ISPs [internet service providers] don't restrict, influence or otherwise meddle with the choices consumers make," Reed Hastings wrote in 2014.
The firm has now said it recognises that subscribers might also want to have greater control over the speeds that Netflix itself provides to mobile ISPs in the first place.
The 600 kilobits per second cap cap it currently enforces is a fraction of the 30 megabits per second download speeds that are now possible over 4G in parts of the UK.
"We will soon introduce a data-saver feature designed for mobile apps," said Netflix spokeswoman Anne Marie Squeo.
"[Users will be able to] either stream more video under a smaller data plan, or increase their video quality if they have a higher data plan."
She added that the feature should become available in May.
Netflix has acknowledged that it restricts the quality of its video streams when it sends them over some mobile data networks.