The lock-out is the latest in the 21-month wrangle to get a new enterprise agreement for the Tahmoor workers.

It is the second time this year that the company has locked out workers and is retaliation against the Construction, Forestry, Mining and Energy Union for its continuing industrial action at the colliery.

Xstrata Coal communications manager James Rickards said the company was well within its rights to respond to industrial action.

``To date the union have taken 3000 hours of industrial action,'' Mr Rickards said.

``Xstrata Coal have taken only 96 hours in responsive action; the last time was in February. The union have had continuous industrial action since June 4.''

Mr Rickards said Xstrata wanted to send a message to the miners that industrial action was not a legitimate negotiating technique.

``This mine needs to be profitable,'' Mr Rickards said.

``And it needs to be viable.''

CFMEU district vice-president Bob Timbs said the new lock-out was particularly disappointing, because less aggressive options were available to Xstrata Coal.

``Xstrata management offered a pay rise, but as we've said time and time again there are far more important things than pay,'' Mr Timbs said.

``Tahmoor mine workers simply want some security that they will not be replaced by contractors and a guarantee that they won't be forced into working 12-hour shifts at the company's discretion. It's really not that much to ask.

``Now Xstrata is trying to grind us down by locking workers out of the colliery until September.''