They were amazed but agreed there was nothing unlawful in what I was doing - they promised to return if they changed their opinion.

New York Real Property Law 235-f, titled "Unlawful Restrictions on Occupancy" provides that it is unlawful for a landlord to restrict occupancy to "a tenant or tenants or to such tenants and immediate family." 

I was advised that the only way to proceed is with an unlawful detainer, and advised to proceed immediately.

We spend a lot of time blaming the other side of the aisle on problems, but real value comes from rolling up your sleeves on a solution.What you are completely missing is that in these places, they are also enacting laws that make it unlawful to discriminate against these prior transgressions.  

Just as a military order is invalid if it's unlawful or unconstitutional.That is not to say you won't get arrested or face a court martial.In the history of our country many sheriffs have disobeyed or didn't enforce laws they believed to be unconstitutional.Alas though our union is imperfect and in the quest for power politicians do pass and enact laws they know or should know won't pass constitutional muster.I heard a talk show host ask the Governor of New Jersey why he thought he had the power to make religious services unlawful.

Eviction records are public records and like the current lawsuit on Seattle's ban on criminal records, it's unlawful to restrict access to them.

I tell them that I fully intend to file an unlawful detainer and that they may not want that on their background search.

Mutual lease termination would have been used, but if they objected to that we would have moved to the next step, eviction for cause.Resident, any members of the resident’s household, or a guest or other person under the resident’s control shall not engage in acts of violence, or threats of violence, including but not limited to the unlawful discharge of firearms, prostitution, criminal street gang activity, intimidation, or any other breach of the housing agreement that the other wise jeopardizes the health safety or welfare of the landlord, his agents, or tenants.VIOLATION OF THE ABOVE PROVISIONS SHALL BE A MATERIAL VIOLATION OF THE HOUSING AGREEMENT AND GOOD CAUSE FOR TEMINATION OF TENANCY.

If they refuse to sign new rental agreement give them your state required notice to vacate (unlawful detainer).

So is this an issue where you were given an illogical (unlawful) reason or how exactly do you feel you were being discriminated against?