Midwives in Northern Ireland are being asked if they are willing to take industrial action over pay.
The ballot by the Royal College of Midwives (RCM) opened on Monday and will close on 29 January.
The union said midwives in Northern Ireland were paid less than their counterparts in Great Britain.
On Wednesday, nurses from the Royal College of Nursing (RCN) will stage their second day of strike action over staffing levels and pay.
The RCM said the ballot came after nine years of pay restraint, with midwives in Northern Ireland currently earning up to £2,000 less than their colleagues in England, with an even wider gap when compared to midwives in Scotland.
“This decision has not been taken lightly,” said Karen Murray, the RCM’s director for Northern Ireland.
“Midwives and maternity support workers in Northern Ireland work incredibly hard to ensure women and their families get safe and high-quality care.
“By paying them less than their colleagues in the rest of GB, the people running our services are taking advantage of their massive contribution, dedication and commitment.
“Demoralised, over-stretched and undervalued staff cannot give the quality of care that women and babies deserve.”
The Department of Health said it did not have the budget or the authority to meet union demands on pay.