Seeking advice: What to do with condo owners not paying HOA?

Hi BP! I own one unit in an 8-unit condo building in Washington DC, which is doing quite well, as I'm renting out to a section 8 tenant. My concern is that our reserves are critically low, because of owners who have been in arrears for years and not paid HOA. I've learned that the non-paying unit owners have acquired their units via the Tenant Opportunity to Purchase Act (TOPA) -- when the rentals were converted to condos, they were able to purchase the units for a bargain, but were not prepared to pay for the recurring costs such as HOAs and special assessments.

We have tried everything to get our non-paying neighbors to pay up, but to no avail. It's been years and they are not being penalized, it also creates an incentive for other neighbors to also not pay.. all at the expense of the upkeep of our building. I'd like to ask for advice -- is there any legal action we can take? I'm open to any suggestions and recommendations -- keep in mind our building reserves are low so we've deferred on decisions that need payment (like hire an HOA lawyer) -- we are open to hearing any ideas, and if we really need a lawyer please help us find an affordable one. Thank you.