Utilities and rail companies are among the corporate sectors most at risk from regulatory or government policy shifts following the upcoming UK general election on 7 May, according to Fitch Ratings.With the Conservative Party having frozen rail fares, and Labour pledging to freeze energy prices if elected, Fitch flagged both sectors as being particularly vulnerable in a note to clients on Friday. The ratings agency also included housebuilders, oil and gas, healthcare and defence companies among those likely to see a challenging operational climate post-elections.Roelof Steenekamp, senior director at Fitch Ratings, said: "Household utility bills have slipped down the political agenda in the last few months due to the improving economy and wage growth overtaking headline inflation, but utilities remain a sector where the political parties' policies vary significantly."A resumption of the rapid growth in bills seen in the first few years of the decade would increase political risk whatever party or combination of parties was in power, he added.In the rail sector, Steenekamp noted that both main parties had some form of policy or the other that would limit an increase in regulated rail fares over the course of the next parliament, with an added complication of a state-owned rail franchise promised by Labour that would be competing with private players for tenders."This could be credit negative for rail franchise operators, even though we do not believe the impact would be significant," he said.Conservative Party policy on housing has focused on providing financial assistance for buyers, for example, through its Help-to-Buy scheme. Such policies tend to push up home prices, which is positive for housebuilders' earnings. However, Fitch said the move could push prices further above their long-term sustainable level, adding to the risk of a bubble and a subsequent correction."Both the Conservative and Labour parties have plans to increase construction, potentially opening up more opportunities for the sector, but we believe house builders could struggle to quickly accelerate construction," Steenekamp added.Fitch reckons healthcare, oil & gas and defence companies could also face reform but any impact would probably be limited as policy shifts would either be incremental or only affect a small portion of their business.