Is it right for a church to require members to give more than 10%?
First, the 10% rule was required by God concerning the Israelites of the O.T. Typically, most churches today who teach tithing proclaim 10% to be a good rule to follow. Although it is required in the O.T., we see giving in a new light in the N.T.
2 Cor. 9:5-7 says:
So I thought it necessary to urge the brethren that they would go on ahead to you and arrange beforehand your previously promised bountiful gift, so that the same would be ready as a bountiful gift and not affected by covetousness. Now this I say, he who sows sparingly will also reap sparingly, and he who sows bountifully will also reap bountifully. Each one must do just as he has purposed in his heart, not grudgingly or under compulsion, for God loves a cheerful giver.
Paul speaks of a bountiful "gift" being collected as promised. (If its required, it's something like... a tax!) Though not encouraged here, "he who sows sparingly" is obviously allowed to do so. Whatever a man decides to give in his heart, Paul does not desire it to be from pressure which can cause members to hold a grudge against the church.
It doesn't appear to be the churches duty to strong arm wallets from member's pockets. It also doesn't appear that they are to "require" giving at all. Giving should be a joyful experience for the wallet holder, and if it can't be, then God can make do without yours.