Workers at Rolls-Royce in Bristol have begun the plant's first strike action in nearly 20 years following the sacking of an Amicus union official.
Jerry Hicks was sacked from his job last month
Tuesday's industrial action by 96 test facility engineers could continue for an indefinite period, the union said.
Jerry Hicks was sacked over misconduct claims, but an employment tribunal provisionally found he had "probably been dismissed on trade union grounds".
The aero-engine maker urged staff to "think carefully" before striking.
A statement from the engineering giant said: "We have a great business in Bristol and would urge employees considering strike action to think carefully whether supporting the unlawful actions of one individual is in their best interests, or those of our customers."
The company said Mr Hicks had been sacked for organising unlawful industrial action earlier in the summer and attempting to undermine disciplinary procedures - claims he denied.
His case is due to appear before a full hearing within six months.
Mr Hicks said: "The company has had several opportunities to resolve this dispute and they can still end it by telephoning me and asking me to return to my job.
"I have never felt so proud in my life at the courage of people prepared to do something on a point of principle, and I have never felt so ashamed of Rolls-Royce.
"The strike will have an immediate impact and it will grow by the hour."
The union Amicus has also called for the full reinstatement of Mr Hicks, who had worked at the plant for 30 years. It also warned it could not rule out the possibility that industrial action could spread.
Around 1,000 workers from the rest of the plant could also be balloted for industrial action.
The Bristol factory produces and services engines for military aircraft, such as the Eurofighter Typhoon, the Hawk and the Harrier.