"difficult to uphold" is a correct and usable phrase in written English.
You can use it to refer to a standard, rule, or value that is hard to maintain or adhere to. For example, "The promise to always put family first is difficult to uphold when one is away for long periods of time."
This tension might make the humane, non-invidious position psychologically unstable, difficult to uphold in situations of conflict and crisis, and politically less efficient.
The popular distinction between vegetable and fruit is difficult to uphold.
Nowadays, facts and truth are becoming increasingly difficult to uphold in politics (and in business and even sports).
Attempts to protect the property rights of slave owners led to increasingly restrictive laws - including laws concerning free blacks - that were difficult to uphold.
But with about 850,000 child labourers in Bolivia and only 78 inspectors, it will be difficult to uphold these protections.
My oncologist in the States allowed me to go to India on the condition I be checked regularly, an agreement I was finding difficult to uphold.
The EPA's proposed 2018 budget slashes protections, and slashes the workforce made up of good and honest people working long and difficult hours to uphold them.
Love relationships are undoubtedly difficult to maintain if we don't consider the steps to uphold a positive dynamic.
"It has been really difficult for us to uphold our family traditions and feel comfortable when we're out in public," the Buena Park salesman said.
Social codes made it difficult for women to uphold the ideal of immaculate neatness and delicacy while enjoying a meal, so the wife of the host often dined in private with her entourage or ate very little at such feasts.
Changing economic conditions may make it difficult for one side to uphold its end of the deal.
