The third season of Westside has seen fewer viewers tune in than previous seasons.
New Zealand on Air says it is getting harder to support local drama, as Filthy Rich and Westside took a ratings hit in their second week on air.
Both Filthy Rich and Westside lost about 30 per cent of their audience this week, after premiering two weeks ago.
Combined, the two series claimed $13.5 million of New Zealand on Air funding, for 2017.
New Zealand on Air spokeswoman Allanah Kalafatelis said it was too early to assess how the series were performing and judgment would be reserved until the full seasons had screened.
"We remain committed to local drama," she told the Weekend Herald.
"It's hard and getting harder, but that's not a reason not to do it. We will keep looking for and supporting the best ideas; we believe there is a place for local stories in amongst the plethora of international options."
Starring Miriama Smith and a cast of young Kiwi actors, Filthy Rich debuted on TVNZ2 last year to lacklustre ratings and critical derision.
Despite the rocky start, NZoA decided to fund a second season, committing $7m to the 14-episode season.
At the time, NZoA defended its decision, saying: "The brilliantly made first series had an average 5-plus audience of 250,000 and a total of more than 700,000 on-demand streams across the series, meeting NZ On Air's objective of a bold local drama engaging its audience."
However, this month's season two premiere attracted just 170,000 viewers, before dropping to 123,000 viewers this week. That marks a 50 per cent decline compared with season one's average audience of 250,000 viewers.
TVNZ director of content Cate Slater acknowledged the numbers were disappointing but said the network remains committed to the series.
"TVNZ's proud to champion local drama and we're fully committed to helping Filthy Rich find as big an audience as it can. We're disappointed this week's numbers are down. We think the show's second series deserves to be enjoyed by a larger audience than it received this week."
Meanwhile, Outrageous Fortune prequel Westside experienced a similar decline this week, as it faced off against the return of Game of Thrones on Monday night.
The series, which screens on Three, saw 200,000 viewers tune into the season three premiere. This week that figure dropped to 141,000 viewers, well below the previous average audience of 220,000 viewers.
The heavily publicised premiere of Game of Thrones season seven screened on Sky SoHo on Monday night - as well as being made available on Sky's on-demand service, Neon.
While Sky doesn't release its programme ratings, a spokesperson confirmed "hundreds of thousands of eyes tuned in".
"Along with most of the rest of the planet, Kiwis were glued to both SoHo and Neon on Monday for Game of Thrones," read a statement.
But any suggestion Three might look to move the NZoA funded series to a less competitive timeslot was dismissed by South Pacific Pictures, which produces Westside.
"There has been no talk of moving the show - nor would we want there to be," said chief executive Kelly Martin.
"The show is performing well - in fact it has won the timeslot both weeks so far in all of its key demographics - despite some tough competition," she said.
Likewise, MediaWorks is standing by the series, with chief content officer Andrew Szusterman saying: "We're really pleased with the performance of Westside ... The results clearly show that Kiwis still place value on watching quality local drama."