Opposition Leader Zed Seselja was critical of two decisions made on Tuesday's first day of debate, a move to increase the size of five key standing committees and a decision to expand the lunch break on sitting days from 90 minutes to two hours.

The decision on committees, to expand their membership from three members to four, will give the government and opposition equal numbers and allow Labor to block moves it disagrees with.

The move will also boost the influence of ACT Greens minister Shane Rattenbury, whose casting vote in the chamber may be needed to break deadlocks.

Mr Seselja said he and his party were unhappy at the shake-up of the committees and he believed Labor meant to hobble the Assembly's ability to scrutinise ministerial conduct for the next four years.

''What we've seen on day one is the Labor-Greens coalition acting like a majority government and not like a hung parliament,'' he said. ''They have chosen to impose a committee system which appears to be designed to have less scrutiny, nobbling the most important committee in the public accounts committee.

''That seems deliberately designed to prevent the opposition from getting information from the government, from properly scrutinising ministers - we will be blocked at every turn by the Labor members on that committee.''

The Liberals' leader said his party would now reconsider its position on parliamentary co-operation with the government, including the granting of pairs for absent MLAs.

''All of these things will be on the table if there is not some level of co-operation,'' Mr Seselja said.

He said the extension of the lunch break undermined any argument for an expanded legislature.

''I'm surprised, given the strong arguments the Labor Party is making about an expanded Assembly, the first things that they have done is to have a very small number of sitting weeks, 13 sitting weeks, and to have longer lunch breaks,'' he said. ''I don't think that's backing up their case that they need more members.''

But Chief Minister Katy Gallagher said the longer break was a necessary move and a return to arrangements that had been in place until 2008.

''We've only had four years when question time started at 2pm and we found practically that it really made it difficult to [do] things in the lunch break - for example, going out to an event,'' she said.

''We will sit for the same amount of hours at the end of the day - this just brings question time back to 2.30pm.

''What we're hearing from the opposition … is that they'd like us to think that they're the hardest working opposition there's ever been in the Assembly, so they're going to speak to motions like this about wanting to work longer, have more sitting weeks.

''But, at the end of the day, when the Assembly is not sitting, the Liberals' car park is empty.''