The National Press Photographers Association's general legal counsel has sent a letter to Amtrak officials asking that railroad "take immediate steps to remedy the railroad's unconstitutional treatment of law-abiding photographers."

The action came after NPPA received complaints over the last few months from photographers who were told by Amtrak police officers that they were not permitted to take photographs of trains or stations. In some instances photographers were threatened with arrest or arrested when they failed to follow officers' commands to delete images.

The issue is likely to be tested in the coming weeks as thousands of media and tourists flood through Union Station in Washington, DC, for the upcoming presidential inaugural.