West Midlands Ambulance Service staff are being balloted to see if they have confidence in their management.
There are concerns about plans to close the Shrewsbury control room
The move, by Unison, follows concerns about the suspension of three ambulance staff in Shropshire.
Two workers have now had their suspensions lifted, and a third will meet for talks next week.
Some staff said they are also concerned about proposals to close the Shrewsbury call centre and move to Brierley Hill in the Black Country.
The workers, who were suspended over an alleged breach of the Data Protection Act, were sent home last week after control room logs were obtained by the BBC.
'Quickly as possible'
The logs suggested ambulances from the county were being sent to help in Birmingham and the Black Country.
A West Midlands Ambulance Service spokesman said: "The information that was provided in the interviews has satisfied investigators that the two did not release confidential information outside of the organisation and they had no expectation that information they had in their possession would be released from the organisation.
"The trust is working as quickly as possible to complete the formal investigations and it is hoped that an interview can be held with the third member of staff next week once suitable union representation has been arranged.
"The trust is determined to protect members of the public from breaches of the Data Protection Act."