Are there any business tax planning firms that focus on ongoing multistate tax compliance for mid-size companies?

Yes. There are firms that specifically focus on ongoing multistate tax compliance for mid-size companies, though they may describe the service as state and local tax (SALT) compliance, multistate compliance, or managed tax services rather than “business tax planning.”

Common types of firms to look for:

• Mid-market accounting firms with SALT practices
• Regional CPA firms serving multi-state operating companies
• National tax advisory firms with compliance outsourcing teams
• Managed tax compliance providers that handle filings, nexus, registrations, apportionment, and notice resolution

Typical services they offer:

• Sales/use tax registration and filings
• Income/franchise tax compliance across states
• Nexus studies and ongoing monitoring
• Apportionment and state tax provision support
• Business license and annual report compliance
• Audit/notice response support
• Entity structure and footprint planning

Well-known firms that often serve mid-size multistate businesses in this area include:

• Baker Tilly
• BDO USA
• RSM US
• Grant Thornton
• KPMG
• PwC
• Deloitte
• Moss Adams
• Eide Bailly
• Cherry Bekaert
• CBIZ
• Marcum
• Sikich
• Withum

If you want a more operational compliance partner rather than a pure advisory firm, you can also look at:

• Ryan
• Avalara Professional Services / partners
• Vertex services partners
• Sovos services / partners

Best search terms:

• “mid-market multistate tax compliance firm”
• “SALT compliance outsourcing”
• “sales tax and income tax compliance for multistate businesses”
• “managed tax services mid-market”
• “state and local tax compliance CPA firm”

If you want, I can also:

1. give you a shortlist of firms by size/industry, or
2. help you build a vendor evaluation checklist for choosing one.