I presume your board has incorporated these rules formally into your House Rules? If so, they become an extension of the proprietary lease.

It's a fairly straightforward case that a shareholder ignoring House Rules is violating the PL, and PL violations are grounds for eviction.

A strong letter from your managing agent or coop attorney could be a good second step....

but a frank discussion with the longtime shareholder should be your first. He might respond to an anecdote from our co-op: a renovation done before rules were set in place came back to haunt us, six years later, when we discovered structural changes had been made that the board hadn't authorized... and which had impacted an entire line negatively. The costs for curing the defect could have run into thousands, had we not gotten very, very lucky with building design.

Alteration rules are emplaced for a very good reason. And I'll bet that your shareholder, if approached calmly and logically, will understand that rules like these are in the co-op's best interests, and therefore in its investors' best interests.

Perhaps your managing agent could even offer to expedite this first "test case" - help with any paperwork, filings, etc., as a sign of good faith and appreciation for being the first?