Unison assistant general secretary Keith Sonnet and MPO acting general manager Rob Newland accused the Department of the Environment, Transport and Regions of being 'out of step' on the Transfer of Undertakings (Protection of Employment) Regulations.
The DETR has said rent officer and support staff moving to the new Rent Officer Agency will not be covered by TUPE because it is an administrative reorganisation.
But the unions say this contradicts assurances from the Department of Trade and Industry that such moves would be covered by the amended Acquired Rights Directive.
The joint statement, the first by both unions, marks the beginning of warmer relations between the two. A protocol for closer working was to have been signed this week, but has been postponed until mid-July.