Last week, grounds maintenance contractor Brophy signed an agreement which formally recognised the rights of GMB employees who transferred to the company from a local authority.
In the next two weeks, the GMB expects to reach similar positions with contractors SITA and BET, as well as two health service contractors. It says this could lead to deals covering most local government tenderers.
This initial agreement covers only 300 GMB members, but the union is confident it can recruit another 700.
A GMB spokesperson said that planned agreements could cover a total of 60,000 people.
GMB national secretary Mick Graham said: 'This contract is recognition of a new relationship between the GMB and private sector companies providing local government services.
'It will not prevent differences of opinion, but it will give us the machinery for resolving them in a more constructive manner.'
Brophy managing director Brian Tranter said: 'This agreement reflects the need for a change from confrontation brought about by CCT to co-operation as the industry enters a new phase of maturity in the provision of quality local authority services.'