In March the Government was defeated when the Lords backed, by 124 votes to 64, a call to delay the proposed sell-off.
But the Commons last month voted, by a majority of 75, to welcome privatisation of the Recruitment and Assessment Services.
The issue is being examined by a Lords Select Committee.
The Labour peers' leader, Lord Richard, condemned the Government's tactics as "disingenuous and, frankly, treating this House with contempt".
He demanded the privatisation be delayed until the Lords committee had reported and the House debated its report. Instead the Government was drawing up a short list of three potential contractors, Lord Richard protested.
"How with one breath the Government do that and with the other breath say they will consider the recommendations of the committee with care and respond in due course is, frankly, beyond me."
Lord Harris of Greenwich (Lib Dem), accused ministers of treating the select committee in an "extraordinary way".Reuse content