The government said petroleum, water, ports and electricity services were declared essential services from midnight Sunday.
Both power and water are state monopolies and petroleum and ports a near-monopoly with only one private operator allowed.
A work-to-rule campaign last week was led by a trade union group connected with the Marxist-nationalist Janatha Vimukthi Peramuna (JVP), a former ally of the country's ruling coalition and the main opposition United National Party.
The Island newspaper said unions connected to last week's action would meet on Monday to decide on further action after some workers were assaulted at Ceylon Petroleum Corporation's distribution centre in Kolonnawa.
Some workers of the Sri Lanka Ports Authority in Colombo had also been also assaulted.
Both utilities are heavily over-staffed.
The newspaper, quoting Sri Lanka port chief Priyath Bandu Wickrema said workers had been offered a 500 rupee monthly increment in basic pay and a 4,000 rupee allo