Non-medical staff in Berkshire and Surrey have gone on strike over fears their jobs will be "privatised".
About 250 members of the Unite and GMB unions at Frimley Health NHS Foundation Trust have started a 48-hour walkout.
But about 300 workers from the Unison union pulled out of strikes.
The trust said its hospitals - Heatherwood and Wexham Park in Berkshire, and Frimley Park in Surrey - were running as normal, and it would explore other "options" with unions.
The strikes by porters, cleaners and security staff were called over the trust's plans for a "money-saving" subsidiary company to run some of its non-clinical services, but unions claimed it was back-door privatisation.
About 90 members from Unite and 160 from GMB have joined the walkout.
But Unison said it postponed industrial action after the trust agreed to halt its plans and explore alternatives.
Unison's regional secretary Steve Torrance said: "This is on the understanding that senior managers at Frimley have agreed to look into alternative solutions, including whether it will be possible to keep the staff employed within the NHS.
"Unison will take no further action for the time being and as a result the trust has agreed not to continue with its existing plans while these other options are pursued."
In a statement the trust said they were exploring alternative plans over its future.
A spokesman for the trust said that as Unison had postponed its industrial action it "will not progress its existing wholly owned subsidiary plans" while "alternative options are fully explored jointly".