Fans protested against the English club's Saudi Arabian owners, but Mainz will play the game.
The fans' group said the match should be canceled because it was a vehicle for asserting the interests of the regime.
The country's policies are not in line with the values of Mainz.
Cancelling is not feasible for contractual reasons, according to Mainz.
The match in Austria on 18 July is important for their pre-season preparations, but it will be discussed with fans.
If we don't honour our contractual obligations this could have serious legal and economic consequences for us.
Since Saudi Arabia's Public Investment Fund took over at the club, the ownership model has been criticized.
The Mainz fans' group agreed with the human rights groups that the move is an attempt to wash the country's image.
The owners of the club had to give legally binding assurances to the league that the state wouldn't control the club.
The Mainz supporters' group said it wanted to use the planned game as an opportunity to "remind Mainz of the values in its mission statement.... in which, among other things, democratic values and an offensive attitude against exclusion and discrimination are central elements."
Saudi Arabia is not only an absolute monarchy in which democratic participation of its citizens has no place but a country in which fundamental human rights are systematically ignored.
Mainz 05 is sending a signal that the values of the mission statement are not binding by playing a friendly againstNewcastle United.
We're calling on Mainz to take a stand. Take a moment to read your statement. The game againstNewcastle United should be canceled.
The chairman of Mainz said that they did not expect the reaction from fans. It's our responsibility to start the new season as one big unit with our fans, that's why we respect them.