Unite leader Len McCluskey has accused Lincolnshire County Council of "failing its public duty" to resolve an ongoing dispute about health visitors' pay.
Since July more than 70 health workers have walked out on numerous occasions for a total of 32 days.
They argue that since the county council took over their contracts from NHS two years ago they haven't had a pay increase, meaning they've lost £2,000 a year.
Speaking at the Community Practitioners’ and Health Visitors’ Association, in Harrogate, earlier Mr McCluskey said the "cash-rich county council' was forcing through a "two-tier system to divide workers".
He said Lincolnshire families with young children are suffering the consequences of a reduced service.
Let me be clear to those council bosses sitting in Lincolnshire county hall. You are failing in your public duty to resolve the impasse and pay your health visitors what is theirs."
Lincolnshire County Council say they have always valued the work of health visitors, are committed to working collaboratively with the workforce and would welcome further constructive talks with Unite.