Are you talking about Luke 11:42? That passage is pretty interesting, because the Pharisees in question were only tithing from their meager "crops" (herbs), and technically completely fulfilling the tithing requirements, because tithes in the OT only came from crops and cattle, not from monetary income. Jesus' response to this, that they "neglect justice and the love of God" is very fitting, as it follows from "But now as for what is inside you—be generous to the poor, and everything will be clean for you."
So when people say, I can't afford to tithe or I'll have nothing to eat, the Biblical response seems to be, they are the ones who receive tithes, not pay them. Because we wouldn't want to see them go unblessed... right? If we say we "bless" Christians "in ministry" with tithes, but insist that the impoverished must "be blessed" only through giving, then don't we risk the warning Jesus gives further along in the passage from Luke 11, Jesus replied, “And you experts in the law, woe to you, because you load people down with burdens they can hardly carry, and you yourselves will not lift one finger to help them. (46)
I am not opposed to Paying 10% of what comes into my home to feed a brother and sister. In fact James says instead of just saying a faith statement by speaking to a persons poverty, "Be filled, Be full and be blessed" Faith will actually take action and feed that person and not just do some prayer.
A women down the street just stopped my wife and asked if she watches kids, she needs to work but even at a cost of 5.00 an hour per Kid, that would eat up her whole days work pay.
So, after the wife and I sought the Lord about it, we believe God asked us to just bless them and watch her kids for free. Something they have never heard of as they don't really go to church.
10% of our money, time and efforts is not often enough though to help someone out. So we just call that sowing, or offering if you want to call it that. I don't want to get into the situation where I am telling God I gave his 10% to feed someone and if they are still hungry, then I did my part.
The tithe is not a law thing, it's a method by which all you are in covenant with God and 10% of what comes in Goes to getting the Word of God out. If that is tomatoes, corn, lemonade stand money, it is whatever you have brought in. This way the devourer has no right to all I bring in and little goes far.
When I first found out about tithing and keeping the enemy out of my finances because everything I made was connected to God in my covenant with him, I have tithed 10%. It was never based on what I had or did not have, 10% goes to God first.
When your money is honoring God first, then it would be impossible to be in lack and do without. You would have to be in stone cold unbelief and disobedience to mess it up.
I have learned that giving God even your rent and bill money when he ask you to help, just makes things a whole lot more easy keeping everything paid and having extra. That would be more sowing though as the tithe is always given before your things are considered.
If at anytime I had to do without or did not have a need met, then I would only recommend tithing to those that could afford it. However, not one time in all these years has God never performed his word for me and not been faithful.
I don't speak lack either though and the Word only.
Blessings.