Angered employees have retaliated with protest lines outside the gates of Esso Australia's Longford plant in the state's east, saying they are are taking a stand against the energy giant's proposed cuts to their working conditions.

Central to the stoush is the company's long-running proposal to switch workers to 14-day shifts on the offshore rigs, instead of the existing seven-day-on, seven-day-off roster arrangement. It is also seeking to slash staffing numbers at its onshore plants.

The ExxonMobil affiliate this week began imposing daily lockouts on more than 200 maintenance workers from its Longford and Long Island Point oil and gas plants and offshore platforms, a decision it says was due to "indefinite, prolonged and sporadic" industrial action being taken by trade union members.

It comes as workers have been engaging in protected strike action including bans on overtime, call-outs and stoppages since the year-long negotiations for a new workplace agreement broke down.

Peter Mooney, of the Electrical Trades Union, said more than 90 per cent of employees had overwhelmingly rejected the company's proposals in a recent secret ballot.

"The company is taking the position that it will continue to press on with its claims – claims that will never be acceptable to our members," Mr Mooney said.

"They are saying they want employees to go to 14:14 rosters, but they are not even willing to entertain fixing up the offshore accommodation, which is four to a room and [with] communal toilets."

Mr Mooney said offshore workers and their families had built their lives around their existing work roster arrangements, and should not be forced to change.

"Our people currently work seven-on, seven-off ... they have set up their whole lives like this."

The daily lockouts at the Bass Strait oil fields blocks maintenance staff from onshore sites for two hours a day, while offshore platforms are blocked for three hours a day.

An ExxonMobil spokesman said Esso had moved to lock out employees because ongoing industrial action made it too difficult for the company to plan and execute maintenance work.

"This will provide greater certainty as to worker availability, and allow Esso to prioritise key maintenance work programs," the spokesman said.

Esso said it had put forward several offers of above-inflation pay rises in exchange for "important productivity improvements" that would be vital to prolong the life of its Gippsland oil and gas operations, and secure long-term employment in the region.

"Most of the improvements are accepted industry practice," the spokesman said.

About 500 Esso employees are covered by the Australian Workers Union, which is subject to a court-ordered injunction for taking unprotected strike action. Those strikes are estimated to have cost millions in lost revenue by cutting production.

AWU state secretary Ben Davis said that while Esso had offered above-CPI wage rises, the trade-offs being sought would jeopardise workplace safety.

"Apart from the two-week-on, two-week-off roster, they want to reduce manning levels onshore to the point that we don't think they could run the plants safely," he said.

"Esso can either choose to continue to ignore the workforce and their unions, or sit down to compromise and find something we can all accept and live with."