Using serial ports under Ubuntu 18

When I attempt to communicate with serial devices using PowerShell in Ubuntu 18, I get an “access denied” message when I try to open the port. I can create the port object with no problem:

$port = new-object system.io.ports.serialport ttyACM0

And I can verify the created port:

Echo $port

…yields all the specifics. But when I try to open the port so that I can begin reading or writing:

$port.open()

…access is denied. Is this a procedural error on my part, or a short-coming in the cross platform PowerShell itself? I’ve tried this with onboard serial ports as well as USB to serial devices with no success.