This is just a test, Netflix says, but one that could eventually lead to higher monthly bills for subscribers.

The streaming TV company, which has more than 125 million subscribers worldwide, is testing a higher-priced premium 'Ultra' subscription in Europe offering 4K Ultra HD video with High Dynamic Range (HDR) quality and the ability to watch on four screens at the same time for 17 Euros (€16.99, or about $20).

That's three Euros higher than the highest-price plan currently offered. Some European consumers were offered the Ultra plan at an even higher price (€19.99 or $23.39).

A potential change that could affect more subscribers — some consumers also saw changes in the current Netflix plans with the Premium plan allowing two simultaneous screens, down from four, and the Standard plan getting one screen, down from two.

Netflix would not provide details about the tests, first reported by Italian Web site TuttoAndroid and CordCutting.com.

However, the company said in a statement given to USA TODAY: "We continuously test new things at Netflix and these tests typically vary in length of time. In this case, we are testing slightly different price points and features to better understand how consumers value Netflix. Not everyone will see this test and we may not ever offer the specific price points or features included in this test."

In the U.S., Netflix's current Premium plan ($13.99) includes 4K Ultra HD video and four simultaneous screens. Netflix has many series available in 4K and several including "Luke Cage" and "Glow" in HDR. In addition to having four times the pixels of HDTVs, 4K TVs that handle HDR also deliver improved contrast, richer colors and increased details. Netflix, which doesn't have an abundance of HDR content, currently doesn't charge for HDR video.

Should the Ultra plan become a reality and Netflix adopt changes in the lower-priced Premium and Standard plans, some U.S. homes with multiple TVs and other screens might be faced with choosing a higher-priced plan and pay $3 to $6 more per month.

As more homes get 4K Ultra HD TVs capable of displaying HDR content — about 31 percent of U.S. homes now have 4K Ultra HD TVs, according to the Consumer Technology Association — some Netflix subscribers would be willing to pay more for the best quality video in the Ultra plan.

But more likely there will be many homes wanting the stream on up to four devices, and need to move up to the Ultra plan for that alone.

Wall Street analysts have said Netflix has some wiggle room for higher prices. During the few months of 2017, Netflix posted its largest three-month growth spurt — 8.3 million new subscribers — despite raising the cost of its most popular plan (the Standard plan with two screens watching simultaneously) by $1 in October 2017. Netflix also increased its Premium plan by $2 to $13.99.

But not every Netflix price increase has gone smoothly. Two years ago, Netflix saw a growth slowdown when it raised the Standard plan price by $2 for new members, while current subscribers got the increase over several months in 2016.

Back in 2011, Netflix lost 800,000 U.S. subscribers when it raised the prices for its plan offering streaming video and DVD rentals from $9.99 to $15.98.