From 14 October the union will attend a hearing to gain permission for a judicial review against health secretary Andrew Lansley. Unison claims Mr Lansley has started to implement his reforms without adequate consultation.
UNISON's head of health, Karen Jennings, said it has a 'very strong case'.
'The government cannot just bulldoze ahead with sweeping changes to the NHS without asking people what they think,' she said.
Meanwhile the union Unite decried the White Paper as 'the biggest onslaught on the health service since 1948,' at the Labour conference in Manchester.