Company X submits a proposal to Organization Y to do some work. Company X, having been in business for quite a while, has a rather extensive list of past clients listed on its web site. Organization Y decides to contact some of the listed clients to ask about their experiences with Company X rather than asking Company X for a list of references.
Some of the organizations contacted aren't very happy to be contacted out of the blue by Organization Y and complain to Company X.
Did Organization Y act inappropriately? I'm not sure, but I tend to think not. Assuming Organization Y can find people in the past-client organizations who were involved in the work done by Company X, doing so seems like prudent research before completing a deal for thousands of dollars.
The state is that great fiction by which everyone tries to live at the expense of everyone else. - Frederic Bastiat