Heads of Tasmanian government-owned businesses will be asked to detail the effects of the Government's annual profit grab, including the impact on their ability to plan ahead.

The performance of Tasmania's 14 government-owned businesses (GBEs) will be put under the microscope in four days of parliamentary committee hearings starting today.

The State Opposition, the Greens and Upper House MPs will use the chance to grill the management of GBEs, including Hydro Tasmania, Forestry Tasmania and Aurora Energy, about the Government's policy to take 90 per cent of their after-tax profits.

Labor leader Bryan Green said he wanted more information about debt levels and borrowings.

"[I want to] understand the pressure, they're being put under pressure by the State Government in relation to the amount they're having to borrow to effectively prop up the state budget," Mr Green said.

Greens Leader Cassy O'Connor said she was concerned paying "massive dividends" to the State Government restricted the businesses' ability to plan ahead.

"There is a real risk that a short-term approach of gouging money out of our government business enterprises by the Liberals will lead to long-term viability problems," she said.

"They will have less money in the bank for example, to deal with future claims if they're the MAIB [Motor Accidents Insurance Board].

"They will have less money in the bank to make sure that our Hydro infrastructure is in top shape."

The Motor Insurance Accidents Board, bus company Metro Tasmania and train operator TasRail will front the parliamentary committee first.

Farmers' water access to be questioned

The State Opposition will also use the hearings to question the Government's decision to allow farmers to access water when they normally would not be allowed to, due to the dry spring.

"[We need to see] whether it's appropriate for water to be let go to farmers when we've got commercially operating business in the water market these days," Mr Green said.

He said business people that had made big investments in water had contacted Labor concerned about the changes.

Mr Green also said he wanted to know what modelling had been done to ensure the state's waterways could cope with more water being taken out.

"Some of our water courses come under enormous pressure which in the end can leave them damaged permanently," he said.