The Magpies are due to face the German side on Monday, July 18, as well as facing 1860 Munich three days earlier.
The Premier League side benefited last term following a £305million takeover deal from the Saudi-backed PIF, however the nation's human rights record has caused quite a stir in the football world.
Supporters of Mainz are the latest club to speak out against the ownership model leading to a request for their club to cancel the pre-season contest.
A statement from Supporters Mainz group read: "Newcastle United is not just a football club, but a vehicle for asserting the interests of a regime that tramples on human rights and whose policies are diametrically opposed to the values and mission statement of Mainz 05.
"In times when authoritarian states, large corporations or billionaires are taking over international football in order to assert their interests, it is no longer possible to separate football and politics.
"With the decision to play a friendly match against Newcastle United, Mainz is sending a signal and not a good one… Mainz is actively offering the Saudi regime a stage and thus indirectly recognising it politically.
"We call on Mainz 05: Take a stand! Read your mission statement! Cancel the game against Newcastle United!"
In response, Mainz said that that wanted to 'seek conversation' with fans, but insisted that the match would go ahead as planned.
However, Mainz manager Bo Svensson insists the issue is not so black and white, asking if those protesting have also stopped watching Disney films, after the Saudi PIF bought the company only to later sell the shares.
Speaking to BILD, he said: "It's not an easy topic. I'm a bit divided, on the one hand, I can understand the arguments, on the other hand, when it comes to football, things are always inflated and made a huge deal of.
"Are the people who are asking for cancellations also doing without Disney films with their children? How far do the consequences go?"
Club chairman Stefan Hoffman added: "This practice match is particularly important for the preparation of the team.
"Therefore, we agreed on this game, taking into account the different perspectives and in the absence of an alternative opponent at this standard and on this match date.
"We didn't expect the reaction from some fans in this form. We respect them and regret that these irritations have arisen because we see it as our responsibility to go into a season with all the fans as a united unit."