Porters abandoned their posts at the Royal Sussex County Hospital in Brighton in support of a suspended colleague.
GMB trade union representative Mick Malloy was suspended on full pay after a complaint by an employee at Brighton and Sussex University Hospitals NHS Trust.
Mr Malloy, who works for ISS Mediclean at the Royal Sussex, was informed of the action on Friday.
Hours later five of his colleagues, due to work the night shift, walked out of the hospital in protest.
The unnamed complainant wrote a letter to the GMB trade union and a copy was also sent to ISS.
Charles Harrity, GMB organiser for Brighton and East Sussex, is today meeting ISS and trust managers to discuss the case.
He says Mr Malloy should not have been suspended because the complaint related to a trade union matter and should have been dealt with by the GMB.
He said: "We are very concerned about this situation because obviously patient care may be put at risk."
The porters are understood to have returned to work during the weekend.
A spokesman for ISS Mediclean said: "I can confirm that following a formal complaint by a trust employee, a member of ISS staff has been suspended on full pay pending a full investigation.
"Members of staff did walk out on Friday night but it is my understanding that patients were not put at risk."
ISS is contracted to provide a portering, cleaning and patient-catering service.
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