SAN FRANCISCO (AP) — Facebook is raising how much it pays U.S. contractors who do some of its most taxing work, including watching violent and other objectionable material for possible removal.

Facebook will pay at least $18 an hour for these jobs. Those in New York City, Washington, D.C., and the San Francisco Bay area will get $22 per hour due to a higher cost of living. Facebook said its minimum pay for all contractors has been $15 per hour.

The content review jobs are psychologically taxing. Facebook has been criticized for not paying the workers enough and not providing enough support. Reports have documented that some of them have been left with post-traumatic stress symptoms from the work.

Facebook said Monday it's also adding tools for content moderators to have graphic images blurred out or shown in black and white before they see it.

The company said it's looking into "similar standards" outside the U.S. but did not say when. Facebook said the pay raise in the U.S. will take effect by mid-2020.

Facebook has been working to boost its use of artificial intelligence to catch objectionable material before people see it, but it's nowhere near being able to do without humans. And even its thousands of human workers can't catch everything. And humans, unlike AI, can feel the effects of looking at the worst of humanity materialize on screen day after day.

Facebook has not disclosed how many contractors it employs. It has said that 30,000 people work on its safety and security teams that includes content moderation, but it is not clear how many of these are contractors.