At first glance, the mood seemed almost cheery despite a damp and muggy morning, two watchful private security guards and a number of security cameras.

But beneath the smell of sizzling sausages and the sound of blokes giving each other a good-natured ribbing, there was determination in the miners' faces.

Many of those assembled said they first heard of the lockout in a letter delivered by courier to their homes.

It was the latest move in a 16-month battle between mining giant and Tahmoor owner XStrata and the CFMEU's Energy and Mining division, over an enterprise agreement the union has said would strip workers of basic entitlements and job security.

Clad in a T-Shirt declaring XStrata to be "condition killers", coal preparation president Bob Timbs said it was important to make clear that the union was not interested in extra money in exchange for conditions.

"We have not talked about remuneration. The campaign is not about remuneration at this stage," he said.

"We refuse to have an agreement that cuts across our right to safety and security in the workplace."

In a statement earlier this week, XStrata Coal western and southern operations manager Dan Clifford said a proposed Enterprise Agreement (EA) would offer workers an average 25 per cent base salary increase over four years.

XStrata Coal communications manager James Rickards said negotiations had stalled after an initial offer for a new agreement.

"Having conducted over 50 meetings with the CFMEU throughout the past 15 months of negotiations, we have now reached an impasse," he said.

"We provided an offer for a new EA in accordance with Fair Work Australia legislation 10 weeks ago and, disappointingly, there has been no movement from the CFMEU.

"As a result, we have now provided notice to all employees that we will be taking the offer to a vote at the end of next week."